Abundance and distribution of antennal sensilla on males and females of three sympatric species of alpine grasshopper (Orthoptera: Acrididae: Catantopinae) in Aotearoa New Zealand

doi:10.21203/rs.3.rs-1962606/v1

Download PDF

Research Article

Abundance and distribution of antennal sensilla on males and females of three sympatric species of alpine grasshopper (Orthoptera: Acrididae: Catantopinae) in Aotearoa New Zealand

https://doi.org/10.21203/rs.3.rs-1962606/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

Brachaspis nivalis, Sigaus australis and Paprides nitidus are grasshopper species endemic to Aotearoa New Zealand where they are sympatric in several regions of South Island. On mountains of Kā Tiritiri o te Moana (Southern Alps), B. nivalis is most abundant on scree/rock habitat whereas S. australis and P. nitidus are prevalent in alpine tussock and herbfields. It is expected, therefore, that these species have different sensory needs that are likely to be apparent in the type, abundance, and distribution of chemo-sensilla on their antennae. It is also likely that sexual selection has resulted in sex linked differences in sensilla. To test these hypotheses, abundance and distribution of the chemo-sensilla on the dorsal and ventral surfaces of their antennae were characterized in adult males and females of the three species. Five types of chemo-sensilla were identified on the distal portion of their antenna: chaetica, basiconica, trichoidea, coeloconica, and cavity. All species had significantly more chemo-sensilla on the ventral than the dorsal surface of antennae and a similar distribution pattern of chemo-sensilla. Despite having relatively short antenna, B. nivalis had the largest number of olfactory sensilla, but the fewest chaetica of the three species studied. A plausible explanation is that B. nivalis prefer less vegetated habitats compared to the other species, and therefore may rely more on olfaction (distance) than taste (contact) reception for finding food. No significant differences were observed between the sexes of B. nivalis and P. nitidus, however, S. australis males had significantly more basiconica sensilla than females.

Acrididae

antenna

sensilla

sexual dimorphism

sympatry

A sensillum is a sensory organ protruding through the impervious exoskeleton of an insect, allowing detection of chemicals, temperature, and movement (e.g., olfactory, gustatory, mechanical, hygro-receptive and thermo-receptive sensilla). In short-horned grasshoppers (Orthoptera, Acrididae), chemical sensitive sensilla are abundant on structures including antennae (Altner et al. 1981; Bland 1989; Chapman 1989; Chen et al. 2003; Greenwood and Chapman 1984; Li et al. 2007; Ochieng et al. 1998; Roh et al. 2020), mouthparts (Blaney and Chapman 1969; Chapman 1989; Jin et al. 2006), legs (Mücke 1991; Yu et al. 2011) and wings (Zhou et al. 2008). The function of each sensilla can be inferred from its shape, size, presence and absence of pores and socket type (Bland 1989; Chapman 1989; Chen et al. 2003; Garza et al. 2021; Li et al. 2007; Nowińska and Brożek 2017). For example, sensilla without pores (aporous) and a flexible socket are considered to be mechanoreceptors, whereas sensilla with pore(s) and an inflexible socket are considered to be chemical receptors (Garza et al. 2021; Li et al. 2007; Nowińska and Brożek 2017; Roh et al. 2020). Chemo-sensitive sensilla can have a single hole (uniporous) at the tip of the projection (apical pore) or have many pores (multi-porous or wall-pored), and these sensilla are responsible for taste (contact chemoreception) and olfaction (distance chemoreception) respectively. The number and proportions of different types of sensilla are likely to be species-specific and comparison of sensilla density and morphology among species can reveal important ecological differences (Nakano et al. 2022).

The abundance of sensilla of various types appears to be related to several ecological factors including the dietary range (i.e., monophagous, oligophagous, polyphagous: Bland 1989; Chen et al. 2003; Zaim et al. 2013), distribution and abundance of resources (i.e., mates and food: Greenwood and Chapman 1984; Ochieng et al. 1998) and sexual communication (i.e., signalers and receivers: Bland 1989; Chen et al. 2003; Li et al. 2021a; Li et al. 2007; Malo et al. 2004; Roh et al. 2016). The inference that the sensitivity of an insect to its external environment depends on the abundance of sensilla (Bland 1989; Chapman 1989) is supported by observations using electro-physiological techniques such as electroantennography (EAG) and single sensillum recordings (SSRs) (Ochieng and Hansson 1999; Chen and Kang 2000; Malo et al. 2004; Li et al. 2021a). For example, the different phases of locusts show characteristic abundance of sensilla on their antenna. Solitarious locusts (at low density) possess more olfactory sensilla (Ochieng et al. 1998) with higher electrophysiological responses to some pheromone components compared to their high density gregarious phase (Ochieng and Hansson 1999). This is possibly because the solitarious locusts require higher olfactory sensitivity to locate conspecifics under low population density compared to the gregarious phase (Hassanali et al. 2005). Sex roles can also play an important role in sensilla abundance and distribution, where receiver (typically males) have higher abundance of sensilla with higher olfactory sensitivity than signallers (typically females), observed in a range of insects including grasshoppers (Chen and Kang 2000), beetles (Li et al. 2021a,b) and moths (Malo et al. 2004). A greater abundance of chemo-receptive sensilla is therefore predicted for those species that live in habitats with sparsely distributed resources and in the sex that is responsible for receiving chemical signals during mating (typically males).

The 12,250 species of grasshoppers (Orthoptera; Caelifera) interact with diverse plant communities around the globe (Husemann et al. 2022; Ibanez et al. 2013; Joern 1979; Welti et al. 2019). However, almost all current knowledge of the chemical exchanges that underpins these plant-insect interactions is derived from the study of a small number of economically important pest species (locusts) (Nakano et al. 2022). In addition to locust species, representatives of a number of Gomphocerinae, Oedipodinae and Melanoplinae, and a few species from Acridinae (Bland 1982, 1989; Chen et al. 2003; Li et al. 2007) have been examined for sensilla but no representatives of the Euryphyminae, Eyprepocnemidinae, Ommatolampidinae, Spathosterninae, Coptacrinae, or southern Catantopinae.

The alpine environment of Aotearoa New Zealand has a rich, endemic ecological community including flightless, acridid grasshoppers (Bigelow 1967; White 1975). These species of southern Catantopinae are the products of an endemic radiation associated primarily with Kā Tiritiri o te Moana, the Southern Alps (Koot et al. 2020). At most locations, several species co-occur on the same plant communities with overlap in their food plants (Watson 1970). Three widespread sympatric species, Brachaspis nivalis (Hutton, 1898), Sigaus australis (Hutton, 1897) and Paprides nitidus (Hutton, 1898), have been shown to have different micro-habitat preferences within scree-shrub-herbfield mosaics (Bigelow 1967; Koot 2018; Watson 1970). Habitat partitioning suggests that these grasshopper species have different sensory requirements relating to the type and distance of cues from potential food plants. Similarly, communication between individual grasshoppers exerts specific demands on sensory ability. The coloring and appearance of these grasshoppers appears to reflect selection on camouflage from predators rather than sexual signals (Fig. 1), and they have reduced wings (tegmina) unsuitable for sound production. Together these limitations in auditory and visual signaling imply that chemical cues may be important for selection of mates as well as food, but direct evidence is lacking.

To explore the chemosensory capabilities of endemic, flightless grasshoppers, we use a comparative approach, hypothesizing that sensilla abundance and distribution among these three species will reflect the putative ecological differences of co-occurring taxa. We focused on antennal sensilla as the antenna is the major location for chemical receptive sensilla (Bland 1989; Chen et al. 2003). We predicted more sensilla on the antennae of B. nivalis that is predominantly in rocky areas of sparse vegetation, compared to S. australis and P. nitidus. We also expected that sexual dimorphism in antennal chemosensory structures would be apparent with males (potential signal-receivers) having higher densities of sensilla than females (Bland 1989; Chen et al. 2003; Li et al. 2007). We quantified the abundance and distribution of chemo-sensilla in male and female B. nivalis, S. australis and P. nitidus.

Insects

Adult grasshoppers of B. nivalis, S. australis and P. nitidus (Fig. 1) were collected during the active summer season on the southeast flank of Hamilton Peak in the Craigieburn Range (43°07'32.7"S 171°41'10.5"E) with approval from the Broken River ski area operators and Department of Conservation (authorization number: 97397-FLO). Insect specimens were frozen then preserved in 99% ethanol. Preservation in high concentration ethanol preserved DNA and effectively dehydrates tissues for microscopy.

Scanning electron microscopy (SEM)

Antennae were examined under scanning electron microscopy (SEM) after being excised from preserved specimens and fixed in fresh 99% ethanol for one to three days to ensure complete dehydration, and then air-dried for two days. Fixed antennae were mounted on aluminum stubs, and gold-coated with a Baltec SCD 050 sputter coater before examination with an FEI Quanta 200 SEM operated in the range of 15–20kV.

Antenna size and sensilla

Antenna morphology was examined under a Leica stereo microscope (SM225, Olympus, Japan) equipped with a digital camera (SC180, Olympus, Japan) and antennal lengths were measured using an imaging software (NIS-Elements 5.01, Nikon Instruments Inc., USA), at The New Zealand Institute for Plant & Food Research Limited, Palmerston North, with permission from Dr. Kambiz Esfandi. The area of each antennal segment was measured using the Measure function on ImageJ/Fiji using SEM images.

Dorsal and ventral surfaces of either left or right antenna of each adult grasshoppers were examined for 10 or 11 males and 10 or 11 females of each species. The surface of antenna was identified by the positioning of the antenna in relation to the antennal groove on the frons (Fig. 2), with the presence of a lenticular organ on the ventral surface of segment 14 and the dorsal surface of segment 20 providing confirmation (Fig. 3a, b: Chen et al. 2003; Bland 1989). These grasshoppers have 23 segments on their antenna, but some individuals have subsections within particular segments (Fig. 3c, d), but we ensured consistent segment numbering by measuring the area of each segment (Table S1). The thirteen distal segments (segments 11 to 23; counting from scape, 23rd being the most distal) are those on which chemo-sensitive sensilla have been reported as abundant in other grasshopper species, whereas the proximal segments have sensilla usually linked to proprioception (Bland 1982, 1989; Chen et al. 2003; Jin et al. 2005; Ochieng et al. 1998). Preliminary observations showed a similar pattern of sensilla distribution in B. nivalis, S. australis and P. nitidus, so all sensilla on these thirteen distal segments were recorded.

Sensilla were classified according to the nomenclature used for the locusts Schistocerca gregaria and Locusta migratoria since these are the most extensively studied taxa (Nakano et al. 2022). Number and size of sensilla were counted and measured using the add-in function Cell Counter and the Measure function respectively on ImageJ/Fiji.

Statistical analysis

All the statistical analyses were performed in the R statistics environment (R Core Team 2020) using the software platform R Studio 4.0.3 (Boston, MA, USA) and graphics are generated using R Studio 4.0.3 and Inkscape 1.2. Statistical normality was tested by the Kolmogorov-Smirnov test before further analysis. Using a student T-test, the body length (mm), antenna length (mm) and segment area (mm²) between species of the same sex, and total number and each type of sensilla recorded on the dorsal and ventral surfaces were compared. Differences in total number and number of each type of sensilla on segments 11 to 23 of the dorsal and ventral surfaces were analyzed among species and sexes of the grasshoppers with a linear model using the lm() function. This was followed by post hoc Tukey honest significant differences for multiple pair-wise comparisons using the emmeans package.

Antennal structure (shape, length, area, and segmentation)

The surface area of each of the thirteen distal segments (11–23) differed among the three species (Fig. 4), although estimates of segment area from 2D images sometimes underestimate as antennae are not flat in some individuals. In particular, the dorsal surface of B. nivalis antennae were often concave (Fig. 3c, d). In all three species, an irregular arrangement of sharply pointed cuticular plates known as the lenticular organ (Fig. 3a, b) was observed on the dorsal surface of the 20th antennal segment and the ventral surface of the 14th segment. The length of antennae ranged between 4.3 and 9.3mm, with S. australis having the longest antennae (male 6.64 ± 0.65mm, female 7.80 ± 0.96mm), and similar lengths observed between P. nitidus (male 5.54 ± 0.33, female 7.32 ± 0.63) and B. nivalis (male 5.51 ± 0.71mm, female 6.83 ± 0.96mm).

No significant difference observed in the antenna length between females of P. nitidus and S. australis (p = 0.22), but significantly longer in S. australis females than B. nivalis females (p = 0.03) and S. australis males than P. nitidus or B. nivalis males (p < 0.01). Most of the segments are significantly larger in males and females of S. australis than other species (Fig. 4, Table S1). This is broadly in proportion with their body size as S. australis specimens were significantly larger in terms of body length (male 21.04 ± 7.20mm, female 31.25 ± 2.88mm) than P. nitidus (male 19.08 ± 1.67mm, female 27.66 ± 2.03mm) or B. nivalis (male 17.68 ± 4.52mm, female 24.47 ± 2.16mm). No significant difference in antenna length was observed between P. nitidus and B. nivalis (P = 0.20 in females, P = 0.90 in males) but some segments were significantly larger in both males and females of B. nivalis compared to P. nitidus (Fig. 4, Table S1). In all three species, females had longer antennae (with larger segments) than conspecific males (Fig. 4, Table S1) which is in keeping with their larger body size (Meza Joya et al. 2022).

Sensilla types, abundance, and distribution

Using sensilla morphology (shape, size, presence/absence of pores, socket types) we recorded five classes of sensilla on the distal antennae segments. These were sensilla chaetica, basiconica, trichoidea, coeloconica and cavity (Fig. 5, Table 1). Within each class of sensillum, size variation was observed (Table 1) and some shape variation was detected in basiconca (Fig. 5c, d) and cavity sensilla (Fig. 5g, h), but no species-specific sensilla or shapes were identified.

Males and females of all three species had significantly more chemo-sensilla on the ventral surface of their antenna than they had on the dorsal surface (Fig. 6a). Three types of olfactory sensilla (basiconica, coeloconica and cavity) were significantly more abundant on ventral surfaces in all species (Fig. 6b, d, e), but significantly more taste sensilla (chaetica) were found on the dorsal surfaces of male and female B. nivalis antenna (Fig. 6f). No class of sensilla was restricted to a single antenna surface, sex, or species.

Table 1

Types of sensilla, probable function and morphological traits observed on the antennae of three species of New Zealand grasshopper. Identification of chaetica, basiconica, trichoidea and coeloconica are based on locusts (Altner et al. 1981; Ochieng et al. 1998) and cavity sensilla are based on a Chinese grasshopper (Li et al. 2007)
Sensillum name	Function	Length (µm)	Basal diameter (µm)	Socket type	Pores	Shape
Chaetica (ch)	Gustation & Mechano-reception	15–30	4–6	Flexible	Apical pore	Long peg-like, ribbed wall (Fig. 5a, b)
Basiconica (ba)	Olfaction	10–18	3.5–5.5	Inflexible	Wall-pored	Short and stout peg-like (Fig. 5c, d)
Trichoidea (tr)	Olfaction	11–15	< 3	Inflexible	Wall-pored	Thin hair-like (Fig. 5e)
Coeloconica (co)	Olfaction & Thermo-reception	2.5–3.5	3–10 (pit diameter)	Inflexible	Wall-pored	Peg contained within a pit (Fig. 5f)
Cavity (ca)	Olfaction	N/A	3–10 (pit diameter)	N/A	N/A	Pit with (Fig. 5h) or without (Fig. 5g) visible tissue

The distribution of the five sensilla types along the antennae were consistent between males and females of B. nivalis, S. australis and P. nitidus (Fig. 7). Taste sensilla (chaetica) were most abundant at the distal end of each antenna (segment 23) (Fig. 7b, h) in all species. For example, the last antennal segment of S. australis had 27–37 chaetica compared to 10–20 on segments 11th to 22nd and a similar pattern was seen in B. nivalis and P. nitidus. Olfactory sensilla consisting of basiconica, coeloconica and cavity were most abundant on the middle antennae segments (especially on 15 to 20; Fig. 7c, e, f, j–l), whereas trichoidea were most abundant on segment 19 or 21 on the dorsal surface (Fig. 7d) and segment 15 on the ventral surface (Fig. 7j).

Comparison of sensilla abundance between species and sexes

The total abundance of sensilla and the proportion of each class on the 13 distal segments of the grasshopper antenna differed between species. Among the three species, B. nivalis had the most chemo-sensilla on their antennae, followed by S. australis and P. nitidus (Fig. 8a, Table S2). Both male and female B. nivalis had significantly more trichoidea than S. australis and P. nitidus (p < 0.001) (Fig. 8d) and B. nivalis males had significantly more coeloconica (p < 0.02) and cavity sensilla than the other species (p < 0.001) (Fig. 8e, f). Brachaspis nivalis and S. australis had significantly more basiconica than P. nitidus (p < 0.001) (Fig. 8c), but S. australis (both males and females) had significantly more chaetica than B. nivalis or P. nitidus (p < 0.001) (Fig. 8b).

Despite female grasshoppers having longer antennae than conspecific males, no significant differences were observed in the total number of chemo-sensilla between the sexes (Fig. 8a), with the exception of S. australis females having fewer basiconica than conspecific males (p = 0.0138) (Fig. 8c). Although not statistically significant, the B. nivalis males examined possessed more olfactory sensilla than their conspecific females (about 15% more trichoidea, 10% more coeloconica and 20% more cavity sensilla) while P. nitidus females had more olfactory sensilla (about 7% more basiconica and 30% more coeloconica) than their conspecific males (Fig. 8c–f, Table S2).

Antennae sensilla have been focused on particular grasshopper subfamilies including Gomphocerinae, Oedipodinae and Melanoplinae, and Acridinae. Our comparative study focused on three sympatric and closely related species of Catantopinae (Koot et al. 2020). Five classes of chemo-sensilla (chaetica, basiconica, trichoidea, coeloconica and cavity) were identified on the antennae of adult males and females of flightless, alpine, grasshopper species endemic to Aotearoa New Zealand. The distribution and abundance of sensilla were very similar in all three species with sensilla significantly more abundant on the ventral surface of their antennae and chaetica more abundant on their tips. We found that B. nivalis had significantly more chemo-sensilla than either S. australis or P. nitidus. No significant differences in numbers of sensilla were observed between sexes of B. nivalis or P. nitidus, however, male S. australis had more basiconic sensilla than conspecific females.

Sensilla types, abundance, and distribution

Chemo-sensilla are diverse in shape with varying numbers of sensory neurons (Altner et al. 1981; Baker et al. 2008; Jin et al. 2006; Ochieng et al. 1998; Romani and Stacconi 2009; Yang et al. 2012; Zhou et al. 2009) and exhibit sensitivity to different chemical compounds (Altner et al. 1981; Cui et al. 2011; Ochieng and Hansson 1999). Four of the five types of chemo-sensilla present in the grasshopper species examined here (chaetica, basiconica, trichoidea, coeloconica and cavity), have been described and studied in Schistocerca gregaria (Cyrtacanthacridinae) and Locusta migratoria (Oedipodinae) locusts (Altner et al. 1981; Cui et al. 2011; Jin et al. 2006; Ochieng et al. 1998; Yang et al. 2012; Zhou et al. 2009). In contrast, cavity sensilla were not observed in locusts (Ochieng et al. 1998), but reported from grasshopper species of other subfamilies; Acrida cinerea (Acridinae), Chrysacris changbaishanensis, Chrysacris jiamusi, Chrysacris heilongjiangensis, Chrysacris liaoningensis, Mongolotettix angustiseptus, Euthystria lueifemora and Chrysochraon dispar (Gomphocerinae) (Li et al. 2007). We identified the rosette of cuticular plates (Bland 1982) or lenticular organ (Bland 1989; Chen et al. 2003), which has previously been recorded on the distal end of antennae in other Acridid species, but its function is unknown.

Sensilla chaetica have contact-chemical and mechano-receptive functions (with their flexible attachments), whereas basiconica and trichoidea are olfactory (Bland 1989; Chen et al. 2003; Cui et al. 2011; Jin et al. 2006; Li et al. 2007; Ochieng et al. 1998). In short-horned grasshoppers, there are two known types of sensilla coeloconica: one with a blunt tipped peg and an apical pore sensitive to temperature and humidity; and the other with a sharp-tipped peg and wall-pores sensitive to temperature and olfaction (Altner et al. 1981). Sensilla coeloconica in the New Zealand alpine grasshoppers have a sharp-tipped peg and are therefore likely to be thermo- and olfactory-receptors. Although electrophysiological examination of cavity sensilla has never been made, these are considered to be olfactory since they have a similar distribution pattern as other olfactory sensilla (Li et al. 2007). Rare, unknown cavity sensillum (Fig. 5h) was detected and this was not observed in other grasshopper species.

We detected size and shape variation within types of sensilla as observed in locusts, where they are interpreted as capable of detecting different chemical stimuli and housing different types of chemosensory neurons and proteins (e.g., chaetica: Zhou et al. 2009; trichoidea: Cui et al. 2011, You et al. 2016), and this may be the case for the alpine grasshoppers studied here.

Few studies have compared the ventral and dorsal surfaces of grasshopper antennae (Bland 1982) or those of other insects (Liu et al. 2021; Romani and Stacconi 2009; Yuvaraj et al. 2018). Comparisons can reveal complex specialization, for example, female mugwort grasshoppers Hypochlora alba (Melanoplinae) have 25% more coeloconica on their ventral surface compared to their dorsal surface, but males of the species have 10% more on the dorsal than the ventral surface (Bland 1982). With the exception of chaetica on B. nivalis antennae, chemo-sensilla were significantly more abundant on the ventral surface compared to the dorsal surface of all three New Zealand alpine grasshopper species.

Patterns of sensilla distribution along the antenna of the three New Zealand alpine grasshoppers were broadly similar to observations of other grasshopper species. For example, high abundance in olfactory sensilla (basicoconica, trichoidea, coeloconica) towards the middle to distal end has been observed in other grasshopper species (Bland 1989; Chapman 1989; Li et al. 2007; Ochieng et al. 1998). At the most distal end of the antenna, sensilla chaetica are most abundant, and therefore it is very likely that this segment is predominantly involved in gustation (contact chemoreception). Watson (1970) observed New Zealand alpine grasshoppers touching plants with their antennae, suggesting that touch (either mechanical or contact-chemoreception) is used for food selection.

Comparison of sensilla abundance between species and sexes

The abundance of sensilla is often linked to species-specific characteristics in the distribution of food and the roles of the two sexes (Bland 1989; Chen et al. 2003; Malo et al. 2004; Li et al. 2007; Li et al. 2021a,b). Notable in this study was how few species or sex-specific differences we detected. We detected few differences when sensilla of S. australis and P. nitidus were compared, however, we found that B. nivalis have distinct sensilla abundance when compared to S. australis or P. nitidus. Brachaspis nivalis have large distal segments although their antennae are the same length as P. nitidus. Enlarged segments at the distal end of antenna facilitates more olfactory sensilla, where B. nivalis have significantly more trichoid sensilla than either S. australis or P. nitidus, and in addition, B. nivalis males have significantly more coeloconica and cavity sensilla than other species. The number of chaetica (gustatory sensilla) in B. nivalis is significantly lower than seen on S. australis antenna. These sensilla differences suggest that B. nivalis may rely more on olfaction (i.e., distance cues) than gustation (i.e., contact cues) in comparison to S. australis. This is consistent with their preference for rocky/scree habitat where food plants are sparse compared to the habitat types of S. australis and P. nitidus (grass or herbfield), where plants are more abundant and continuous (Bigelow 1967; Koot 2018; Watson 1970). On scree slopes B. nivalis may need to rely more on long-range signals than short-range signals to find food sources. Both S. australis and P. nitidus are commonly found in mixture of shrub, herb and scree habitats than scree-only habitats (Koot 2018; Watson 1970) but S. australis (both males and females) have significantly more chemo-sensilla on their antennae than P. nitidus. Paprides nitidus antennae are also shorter and have significantly smaller segments than those of S. australis.

In many grasshopper species males have more sensilla on their antennae than females (80% of 75 species examined by Bland 1989, Chen et al. 2003 and Li et al. 2007). These sexual differences are attributed to sexual selection on males to have high sensitivity to pheromones released by females (Chen et al. 2003; Malo et al. 2004; Wee et al. 2016; Li et al. 2021b). As the New Zealand alpine grasshoppers tend to be visually cryptic (to avoid visual predators) and do not generate acoustic signals with wings when searching for mates (Watson, 1970; personal observation), we expect chemical communication to be important in all three species. In the present study, however, the number of sensilla displayed by males and females differed very little. We did find that male S. australis had significantly more basiconica than females. Basiconica, also called short basiconica (Bland 1989; Chen et al. 2003) or basiconic sensillum I-V (Li et al. 2007) have been reported as more abundant in males of other species belonging to Melanoplinae, Cyrtacanthacridinae, Oedipodinae, Gomphocerinae, northern Catantopinae, Pamphaginae and Acridinae, with 36/55 species examined by Bland (1989), all 12 species by Chen et al. (2003), and all eight species by Li et al. (2007). Although not statistically different, male B. nivalis had more olfactory sensilla (trichoidea, coeloconica, and cavity sensilla) than their conspecific females despite having smaller antenna. Males of other Acridid species also have more coeloconica (> 80% of 75 species examined by Bland 1989, Chen et al. 2003, Li et al. 2007) and cavity sensilla (all eight species examined by Li et al. 2007) than females. Sex-biased abundance of trichoid sensilla shows no constant pattern within taxa (called slender and short basiconic by Bland 1989 and Chen et al. 2003). Sex-biased abundance of sensilla type may be due to sex-specific requirements to detect particular stimuli such as sex pheromones and oviposition-site selection (Rai et al. 1997; Chen et al. 2003; Malo et al. 2004; Wee et al. 2016; Roh et al. 2020; Li et al. 2021b).

No significant difference was observed between male and female P. nitidus although females usually had more basiconica and coeloconica than males. An equal number of sensilla with similar olfactory sensitivity between sexes have also been observed in A. barbensis, because these grasshoppers rely on visual and auditory cues when finding mates (Chen and Kang 2000). However, solitarious S. gregaria males showed higher electrophysiological responses to potential sex pheromones than solitarious females (Ochieng and Hansson 1999) despite the equal abundance of sensilla in males and females (Ochieng et al. 1998). Detailed investigations using neurological and electro-physiological studies are therefore required to further characterize sexual differences in the olfactory sensitivity and functional diversity of sensilla. All three grasshopper species studied here have relatively large eyes, and it is possible despite their disruptive and camouflage coloring that they signal visually to one another. This study serves as a base for further behavioral and electrophysiological (electroantennography or single sensillum recordings) studies to elucidate the chemical ecology of endemic New Zealand grasshoppers and contribute to understandings of their evolution and diversity.

Funding Miss E. L. Hellaby Indigenous Grassland Research Trust

Conflicts of interest/Competing interests Not applicable

Availability of data and material The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request

Code availability (software application or custom code) Inkscape 1.0, R Studio 4.0.3

Authors' contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Mari Nakano. The first draft of the manuscript was written by Mari Nakano and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Acknowledgements

The work was supported by funding from the Miss E. L. Hellaby Indigenous Grassland Research Trust. We are very grateful to Dr. Matthew Savoian, Raoul Solomon and Yanyu He at the Manawatu Microscopy and Imaging Centre (MMIC), Massey University, for technical assistance and advice with a scanning electron microscope (SEM). We would like to acknowledge Claire Newell (Broken River Marketing Coordinator, Broken River Ski Area) for the permission of access to the ski field for grasshopper collections. We would like to thank Dr. Emily Koot (Scientist, Molecular & Digital Breeding, Plant and Food Research) for her contribution in grasshopper collection, Dr. Evans Effah (Junior Research Officer, School of Natural Sciences, Massey University) and Leo Meza Joya (Ph.D. student, School of Natural Sciences, Massey University) for their advice in statistical analyses and supports in fieldwork, and Dr. Kambiz Esfandi, (Team leader, Adaptive Entomology Group, Plant and Food Research), and Jay Liu (Ph.D. student, School of Natural Sciences, Massey University) for their critical comments.

Altner H, Routil C, Loftus R (1981) The structure of bimodal chemo-, thermo-, and hygroreceptive sensilla on the antenna of Locusta migratoria. Cell Tissue Res 215:289–308. https://doi.org/10.1007/BF00239116
Baker GT, Xiong C, Ma PWK (2008) Labial tip sensilla of Blissus leucopterus leucopterus (Hemiptera: Blissidae): ultrastructure and behavior. Insect Sci 15:271–275. https://doi.org/10.1111/j.1744-7917.2008.00210.x
Bigelow RS (1967) The grasshoppers(acrididae) of New Zealand : their taxonomy and distribution. University of Canterbury, Christchurch
Bland RG (1989) Antennal sensilla of Acrididae (Orthoptera) in relation to subfamily and food preference. Ann Entomol Soc Am 82:368–384. https://doi.org/10.1093/aesa/82.3.368
Bland RG (1982) Morphology and distribution of sensilla on the antennae and mouthparts of Hypochlora alba (Orthoptera: Acrididae). Ann Entomol Soc Am 75:272–283. https://doi.org/10.1093/aesa/75.3.272
Blaney WM, Chapman RF (1969) The fine structure of the terminal sensilla on the maxillary palps of Schistocerca gregaria (Forskål) (Orthoptera, Acrididae). Zeitschrift für Zellforsch und Mikroskopische Anat 99:74–97. https://doi.org/10.1007/BF00338799
Chapman RF (1989) The chemosensory system of the monophagus grasshopper, Bootettix argentatus Bruner (Orthoptera: Acrididae). Int J Insect Morphol Embryol 18:111–118
Chen H, Kang L (2000) Olfactory responses of two species of grasshoppers to plant odours. Entomol Exp Appl 95:129–134. https://doi.org/10.1046/j.1570-7458.2000.00650.x
Chen H, Zhao YX, Kang L (2003) Antennal sensilla of grasshoppers (Orthoptera: Acrididae) in relation to food preferences and habits. J Biosci 28:743–752. https://doi.org/10.1007/BF02708435
Cui X, Wu C, Zhang L (2011) Electrophysiological response patterns of 16 olfactory neurons from the trichoid sensilla to odorant from fecal volatiles in the locust, Locusta migratoria manilensis. Arch Insect Biochem Physiol 77:45–57. https://doi.org/10.1002/arch.20420
Garza C, Ramos D, Cook JL (2021) Comparative morphology of antennae in the family Pleidae (Hemiptera: Heteroptera). Zoomorphology 140:243–256. https://doi.org/10.1007/s00435-021-00522-8
Greenwood M, Chapman RF (1984) Differences in numbers of sensilla on the antennae of solitarious and gregarious Locusta migratoria L. (Orthoptera: Acrididae). Int J Insect Morphol Embryol 13:295–301. https://doi.org/10.1016/0020-7322(84)90004-7
Hassanali A, Njagi PGN, Bashir MO (2005) Chemical ecology of locusts and related acridids. Annu Rev Entomol 50:223–245. https://doi.org/10.1146/annurev.ento.50.071803.130345
Husemann M, Dey LS, Sadílek D, et al (2022) Evolution of chromosome number in grasshoppers (Orthoptera: Caelifera: Acrididae). Org Divers Evol. https://doi.org/10.1007/s13127-022-00543-1
Ibanez S, Lavorel S, Puijalon S, Moretti M (2013) Herbivory mediated by coupling between biomechanical traits of plants and grasshoppers. Funct Ecol 27:479–489. https://doi.org/10.1111/1365-2435.12058
Jin X, Brandazza A, Navarrini A, et al (2005) Expression and immunolocalisation of odorant-binding and chemosensory proteins in locusts. Cell Mol Life Sci 62:1156–1166. https://doi.org/10.1007/s00018-005-5014-6
Jin X, Zhang SG, Zhang L (2006) Expression of odorant-binding and chemosensory proteins and spatial map of chemosensilla on labial palps of Locusta migratoria (Orthoptera: Acrididae). Arthropod Struct Dev 35:47–56. https://doi.org/10.1016/j.asd.2005.11.001
Joern A (1979) Feeding patterns in grasshoppers (Orthoptera: Acrididae): factors influencing diet specialization. Oecologia 38:325–347. https://doi.org/10.1007/BF00345192
Koot EM (2018) The ecology and evolution of New Zealand’s endemic alpine grasshoppers. Dissertation, Massey University
Koot EM, Morgan-Richards M, Trewick SA (2020) An alpine grasshopper radiation older than the mountains, on Kā Tiritiri o te Moana (Southern Alps) of Aotearoa (New Zealand). Mol Phylogenet Evol 147:. https://doi.org/10.1016/j.ympev.2020.106783
Li N, Ren BZ, Liu M (2007) The study on antennal sensilla of eight Acrididae species (Orthoptera: Acridoidea) in Northeast China. Zootaxa 1544:59–68. https://doi.org/10.11646/zootaxa.1544.1.3
Li YY, Liu D, Wen P, Chen L (2021a) Detection of volatile organic compounds by antennal lamellae of a scarab beetle. Front Ecol Evol 9:1–8. https://doi.org/10.3389/fevo.2021.759778
Li YY, Shao KM, Liu D, Chen L (2021b) Structure and distribution of antennal sensilla in Pseudosymmachia flavescens (Brenske) (Coleoptera: Scarabaeidae: Melolonthinae). Microsc Res Tech 1588–1596. https://doi.org/10.1002/jemt.24020
Liu YQ, Li J, Ban LP (2021) Morphology and distribution of antennal sensilla in three species of Thripidae (Thysanoptera) infesting alfalfa Medicago sativa. Insects 12:1–14. https://doi.org/10.3390/insects12010081
Malo EA, Castrejón-Gómez VR, Cruz-López L, Rojas JC (2004) Antennal sensilla and electrophysiological response of male and female Spodoptera frugiperda (Lepidoptera: Noctuidae) to conspecific sex pheromone and plant odors. Ann Entomol Soc Am 97:1273–1284. https://doi.org/10.1603/0013-8746(2004)097[1273:ASAERO]2.0.CO;2
Meza Joya FL, Morgan-Richards M, Trewick SA Relationships among body size components in New Zealand flightless grasshoppers (Orthoptera: Acrididae) and their ecological applications. J Orthoptera Res
Mücke A (1991) Innervation pattern and sensory supply of the midleg of Schistocerca gregaria (Insecta, Orthopteroidea). Zoomorphology 110:175–187. https://doi.org/10.1007/BF01633002
Nakano M, Morgan-Richards M, Trewick SA, Clavijo-McCormick A (2022) Chemical ecology and olfaction in short-horned grasshoppers (Orthoptera : Acrididae). J Chem Ecol 48:121–140. https://doi.org/10.1007/s10886-021-01333-3
Nowińska A, Brożek J (2017) Morphological study of the antennal sensilla in Gerromorpha (Insecta: Hemiptera: Heteroptera). Zoomorphology 136:327–347. https://doi.org/10.1007/s00435-017-0354-y
Ochieng SA, Hallberg E, Hansson BS (1998) Fine structure and distribution of antennal sensilla of the desert locust, Schistocerca gregaria (Orthoptera: Acrididae). Cell Tissue Res 291:525–536. https://doi.org/10.1007/s004410051022
Ochieng SA, Hansson BS (1999) Responses of olfactory receptor neurones to behaviourally important odours in gregarious and solitarious desert locust, Schistocerca gregaria. Physiol Entomol 24:28–36. https://doi.org/10.1046/j.1365-3032.1999.00107.x
R Core Team (2022) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.r-project.org/index.html%0A
Rai MM, Hassanali A, Saini RK, et al (1997) Identification of components of the oviposition aggregation pheromone of the gregarious desert locust, Schistocerca gregaria (Forskal). J Insect Physiol 43:83–87. https://doi.org/10.1016/S0022-1910(96)00051-0
Roh GH, Lee YJ, Park CG (2020) Morphology and distribution of antennal sensilla in a parasitoid fly, Gymnosoma rotundatum (Diptera: Tachinidae). Microsc Res Tech 83:589–596. https://doi.org/10.1002/jemt.23449
Roh HS, Park KC, Oh HW, Park CG (2016) Morphology and distribution of antennal sensilla of two tortricid moths, Cydia pomonella and C. succedana (Lepidoptera). Microsc Res Tech 79:1069–1081. https://doi.org/10.1002/jemt.22747
Romani R, Stacconi MVR (2009) Mapping and ultrastructure of antennal chemosensilla of the wheat bug Eurygaster maura. Insect Sci 16:193–203. https://doi.org/10.1111/j.1744-7917.2009.00271.x
Watson RN (1970) The feeding behaviour of alpine grasshoppers (Acrididae : Orthoptera), in the Craigieburn Range, Canterbury, New Zealand. Dissertation, University of Canterbury
Wee SL, Oh HW, Park KC (2016) Antennal sensillum morphology and electrophysiological responses of olfactory receptor neurons in trichoid sensilla of the diamondback moth (Lepidoptera: Plutellidae). Florida Entomol 99:146–158. https://doi.org/10.1653/024.099.sp118
Welti EAR, Qiu F, Tetreault HM, et al (2019) Fire, grazing and climate shape plant–grasshopper interactions in a tallgrass prairie. Funct Ecol 33:735–745. https://doi.org/10.1111/1365-2435.13272
White EG (1975) A survey and assessment of grasshoppers as herbivores in the South Island alpine tussock grasslands of New Zealand. New Zeal J Agric Res 18:73–85. https://doi.org/10.1080/00288233.1975.10430390
Yang Y, Krieger J, Zhang L, Breer H (2012) The olfactory co-receptor Orco from the migratory locust (Locusta migratoria) and the desert locust (Schistocerca gregaria): identification and expression pattern. Int J Biol Sci 8:159–170. https://doi.org/10.7150/ijbs.8.159
You Y, Smith DP, Lv M, Zhang L (2016) A broadly tuned odorant receptor in neurons of trichoid sensilla in locust, Locusta migratoria. Insect Biochem Mol Biol 79:66–72. https://doi.org/10.1016/j.ibmb.2016.10.008
Yu Y, Zhou S, Zhang S, Zhang L (2011) Fine structure of the sensilla and immunolocalisation of odorant binding proteins in the cerci of the migratory locust, Locusta migratoria. J Insect Sci 11:1–10. https://doi.org/10.1673/031.011.5001
Yuvaraj JK, Andersson MN, Anderbrant O, Löfstedt C (2018) Diversity of olfactory structures: a comparative study of antennal sensilla in Trichoptera and Lepidoptera. Micron 111:9–18. https://doi.org/10.1016/j.micron.2018.05.006
Zaim A, Petit D, Elghadraoui L (2013) Dietary diversification and variations in the number of labrum sensilla in grasshoppers: which came first? J Biosci 38:339–349. https://doi.org/10.1007/s12038-013-9325-8
Zhou SH, Zhang J, Zhang SG, Zhang L (2008) Expression of chemosensory proteins in hairs on wings of Locusta migratoria (Orthoptera: Acrididae). J Appl Entomol 132:439–450. https://doi.org/10.1111/j.1439-0418.2007.01255.x
Zhou SH, Zhang SG, Zhang L (2009) The chemosensilla on tarsi of Locusta migratoria (Orthoptera: Acrididae): distribution, ultrastructure, expression of chemosensory proteins. J Morphol 270:1356–1363. https://doi.org/10.1002/jmor.10763

No competing interests reported.

SupplementaryInformation.docx

Download PDF

Editorial decision: Major revision
07 Oct, 2022
Reviews received at journal
22 Aug, 2022
Reviewers agreed at journal
19 Aug, 2022
Reviewers agreed at journal
16 Aug, 2022
Reviewers invited by journal
16 Aug, 2022
Submission checks completed at journal
16 Aug, 2022
Editor assigned by journal
16 Aug, 2022
First submitted to journal
15 Aug, 2022

You are reading this latest preprint version

Abundance and distribution of antennal sensilla on males and females of three sympatric species of alpine grasshopper (Orthoptera: Acrididae: Catantopinae) in Aotearoa New Zealand

Status:

Version 1

Abstract

Figures

Introduction

Materials And Methods

Insects

Scanning electron microscopy (SEM)

Antenna size and sensilla

Statistical analysis

Results

Antennal structure (shape, length, area, and segmentation)

Sensilla types, abundance, and distribution

Comparison of sensilla abundance between species and sexes

Discussion

Sensilla types, abundance, and distribution

Comparison of sensilla abundance between species and sexes

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1