The golden jackal (Canis aureus) is a canid species broadly distributed across Europe, including Hungary, where its population has increased exponentially in recent decades. Despite its expanding range and ecological relevance, comprehensive morphometric studies on the golden jackal in Hungary are lacking. Skull and body morphologies represent population/individual traits, genetic distances, environmental impacts, and growth variables, making morphological study essential. We conducted Hungary's first comprehensive body and skull morphometry examination of golden jackals.Between January 2021 and January 2023, we performed morphometric measurements on 754 golden jackals at two developmental stages, juveniles and adults, of different sexes (male and female) in Somogy County, Hungary. We found evidence of sexual dimorphism in all seven body measurements, which were greater in males than in females. We also demonstrated sexual dimorphism in most craniometric measurements (19/21), which were also larger in males. Most skulls differed significantly in size between the sexes and age groups, whereas postoperative breadth and foramen magnum height were not significantly different. Our results can contribute to a better understanding the ecology, behavior, and adaptation of golden jackals in the overpopulated Hungarian habitat, providing valuable insights for future conservation and management efforts."
Short Report
Morphometric Variations in Golden Jackal (Canis aureus) in Somogy County, Hungary
https://doi.org/10.21203/rs.3.rs-3559711/v1
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canid species
skull
body morphometry
golden jackal
sexual dimorphism
In the last three decades, the golden jackal population in Europe has significantly increased in number and geographical range (Arnold et al. 2012; Trouwborst et al. 2015; Jirků et al. 2018). The golden jackal population has exponentially increased since the early 1990s., in Hungary. Its opportunistic and generalist diet, flexible movement, and mating behaviour presumably promote its rapid spread (Lanszki et al. 2018; Hatlauf et al. 2021; Csányi et al. 2023). Carnivores are highly variable in several aspects, such as size, diet, social behaviour, movement behaviour, and activity patterns (Gittleman 1985; Meiri et al. 2005); among them, variation in body size is probably one of the most significant characteristics of any animal (Gortázar et al. 2000). In carnivores, variations in body dimensions and skull size have also been recognised to exhibit differences between the sexes and across regions (Meiri et al. 2005). The dimensions of the body and skull of mammalian predators have a significant impact on various characteristics, such as basal metabolism, communication, social hierarchy, reproductive characteristics, reproductive success (Geffen et al. 1996; Harrington and Asa 2003; Packard 2003; MacNulty et al. 2009). Morphometric data are often used to assess interspecies and intraspecies variation, as variations in cranial features are not solely attributable to environmental factors and anatomical variations but also have a genetic background (Basto et al. 2016).
Golden jackals' cranial and body size have only been analysed in a few locations across their geographic range in Europe. Body and skull measurements were carried out in the Czech Republic: n = 1 (Koubek et al. 2007) and Ukraine (body: n = 42, skull: n = 40) (Volokh and Roženko 2016); body size measurements were carried out in Croatia and Serbia: n = 66; n = 16 (Boskovic et al. 2015), Croatia: n = 50 (Rezić et al. 2017), Bulgaria: n = 262 (Raichev et al. 2017), and Russia: n = 1 (Rykov et al. 2022). Craniometric data are available from Croatia: n = 15 (Kryštufek and Tvrtković 1987), Bulgaria: n = 228 (Stoyanov 2020), Hungary: n = 19, Bulgaria n = 21, and Western Europe n = 7 (Hatlauf et al. 2021), Bosnia and Herzegovina: n = 11 (Hadžiomerović et al. 2022), and Serbia: n = 296 (Porobić et al. 2016).
The present study simultaneously analysed the skull and body dimensions and assessed the differences between sexes and ages. This study is novel because it is the first morphometric analysis of golden jackals in Hungary with both body and skull measurements and the first of such sample size to simultaneously report body and skull measurements in Europe.
The obtained morphometric data of the golden jackal provide valuable information for studying its taxonomy, evolutionary history, ecological adaptations, conservation efforts, and other biological and behavioural aspects.
Jackals were collected from hunting management areas in Somogy County in the Pannonian biogeographical region of southwestern Hungary. The study area is between Lake Balaton and the Drava River, a flat lowland with dunes and an average height of 173 m a.s.l., dominated by natural and semi-natural habitats. The area's continental climate is characterized by moderately humid and mild winters. The annual mean temperature is 10.3 ºC; precipitation is 700–750 mm (Lanszki et al. 2018a).
The studied mesopredator is the largest mammalian predator in the area, whose population has increased exponentially in recent decades. Six golden jackals were harvested in Hungary in 1995 and the number of harvested individuals increased to 14,831 by 2022 (Csányi et al. 2022).
In Hungary, according to the current hunting law, the golden jackal is a species that can be legally hunted all year round. No animals were killed specifically for this study.
In total, 754 golden jackals (379 females and 355 males) were collected from the study area (Fig. 1).
After biometric characterisation, the weight and sex were recorded. The individuals were divided into two age categories: juveniles (younger than one year) and adults (one year and older). The body weight (W) of each jackal was determined in kilograms. Six additional body dimensions were measured to the nearest millimetre using a measuring tape: body length from the anterior tip of the nose pad to the end of the tail (HB), tail length (TL), head length (HL), wither height (WH), hind foot (left) length (HF), and neck circumference (NC); (cm).
After measuring the body dimensions, most soft tissues were first removed to clean the heads, and the skulls were subsequently boiled to remove the remaining tissues and avoid causing any damage (Sullivan and Romney 1999).
Twenty-one dimensions were obtained for each skull using an INSIZE digital caliper with 0.01 precision. The following morphometric parameters were measured: (1) ventral total length (VL); (2) skull length from the os nasale to prostion (LNP); (3) total skull length (TSL); (4) condylobasal length (CBL); (5) basal length (BL); (6) palatal length (PL); (7) length of the upper tooth row (LUT); (8) length of the upper tooth row (LUT2); (9) zygomatic width (ZW); (10) mastoid width (MW); (11) interorbital width (IW); (12) postorbital breadth (PB); (13) cranial length (CL); (14) nasal length (NL); (15) cranial width (CW); (16) length of the lower tooth rows from C to M2 (LCT); (17) total mandibular length from alveolus I to the processus condyloideus (TML); (18) mandible length (ML); (19) foramen magnum width (FMW); (20) foramen magnum height (FMH); (21) height of the occipital triangles (HOT) (Fig. 2).
Statistical analyses
Descriptive statistics (mean, standard deviation (SD), standard error (SE), and minimum and maximum values) were calculated for body dimensions and craniometric measurements of all golden jackal samples. Furthermore, principal component analysis (PCA) was performed to assess the intraspecific differences among golden jackal craniometric measurements. IBM SPSS Statistics Version 25 (IBM Corp. 2017) performed the PCA.
The golden jackal biometric and skull measurements were analysed to assess the differences and variations in sex and age. The data were first tested to confirm the normality of the distribution. The central limit theorem was followed as our sample group comprised more than 100 individuals. The homogeneity of variances was tested by Levene’s test (Levene 1961). The majority of the data exhibited homogenised variance, as shown by a p-value greater than 0.05 in Levene's test, however there were a few instances where this was not the case. The analyses were conducted using the obtained results.The mean values of each dimension were thereafter subjected to a comparative analysis between the sexes (females and males) and age groups (adults and juveniles) using Student's t-test (Zar, 1999). When the premise of homogeneity of variances was not met, the Student's t-test was employed, taking into account the absence of equal variances. Our results were also confirmed using the Mann–Whitney U test because some of our variables showed a non-normal distribution, as tested using the Shapiro–Wilk test (Shapiro and Wilk 1965). The relationship between some body dimensions and craniometric measurements was also tested with a linear correlation (Pearson’s correlation test) and illustrated using a scatter diagram. We used The JASP software (version 0.14.1) (JASP Team 2020) for all statistical analyses.
The principal component analysis (PCA) conducted on the craniometric measurements of the golden jackal, after eliminating any missing data, revealed that the first two principal components (PC1 and PC2) accounted for 65% of the total variance (Fig.3). Principal Component 1 (PC1) and Principal Component 2 (PC2) accounted for 58% and 7% of the observed variance, respectively. Of the 21 craniometric measurements, 16 contributed almost exclusively to the variation in PC1; these included VL, LNP, TSL, CLL, BL, PL, LUT, LUT2, ZW, MW, IW, CL, NL, LLT, UML, and ML. The remaining five measurements (PB, FMH, FMW, CW, and HOT) explained the variation in PC1 and PC2 (Fig.3).
Despite the absence of clear delineation between male and female groups in our findings, a majority of males (74.9%) occupied the right side of the YY axis, while most females (71.5%) were on the left side of the YY axis. This observation suggests that males tend to exhibit bigger sizes compared to females, as shown by the PC1 analysis (Fig.4). In a similar vein, discernible categories based on age, such as adults or juveniles, were absent. The data indicates that a majority of adults (61.1%) were situated on the right side of the YY axis, whereas a majority of juveniles (63.9%) were located on the left side of the YY axis. This observation suggests that adults tend to have greater sizes than juveniles, as inferred from the PC1 analysis. (Fig.5).
Our golden jackal measurements confirmed the presence of sexual dimorphism, as indicated in previous studies (Kryštufek and Tvrtković 1987; Demeter and Spassov 1993; Van Valkenburgh and Wayne 1994; Stoyanov 2012; Porobić et al. 2016; Markov et al. 2017). In our study, sexual dimorphism in the golden jackal body size was evident, with all body measurements showing statistically significant results (Table 1). For all body measurements, our results showed that males were, on average, 5,68% bigger than females (Table 1).
Our findings also demonstrated sexual dimorphism in skull size. For most craniometric measurements, our results showed that males were, on average, 3,21% bigger than females (Table 1), as suggested by the PCA (Fig. S4). Regarding the skull measurements, two dimensions, namely PB and FMH, were not significantly different between the sexes (Table 1).
Table 1: Results of the statistical analysis of craniometrical and body measurements (sex and age categories, males and females)
The golden jackal is a flexible species in terms of its distribution and population growth, which allows the study of rapid evolutionary changes in different habitats and climates. The novelty of our study lies in the simultaneous examination of body and skull dimensions in a large sample size, providing a significant basis for studying the taxonomy of carnivores.
Conflict of interests
The authors have no conflicts of interest to declare.
Acknowledgments
The SEFAG ZRT.’s professional hunters, mainly Mihály Horváth, provided the jackals and helped with body measurements. We thank the Dél-Dunántúli Fauna Vt.’s colleagues for their assistance in skull cleaning and Roland Szabó, Evelin Buzsáki, Kristóf Kámán, and Kristóf László Tóth for contributing the skull images.
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