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- Heterochrony of puberty in the European badger (Meles meles) can be explained by growth rate and group-size: Evidence for two endocrinological phenotypes
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Puberty is a key stage in mammalian ontogeny, involving endocrinological, physiological and behavioural changes, moderated by intrinsic and extrinsic factors. Thus, not all individuals within one population achieve sexual maturity simultaneously. Here, using the European badger (Meles meles) as a model, we describe male testosterone and female oestrone profiles (using Enzyme-immunoassays) from first capture (3 months, post-weaning) until 28 months (attaining sexual maturity and final body size), along with metrics of somatic growth, scent gland development and maturation of external reproductive organs as well as intra-specific competition. In both sexes, endocrinological puberty commenced at ca. 11 months. Thereafter, cub hormone levels followed adult seasonal hormone patterns but at lower levels, with the majority of cubs reaching sexual maturity during their second mating season (22–28 months). Interestingly, there was evidence for two endocrinological phenotypes among male cubs (less evident in females), with early developers reaching sexual maturity at 11 months (first mating season) and late developers reaching sexual maturity at 22–26 months (second mating season). Early developers also attained a greater proportion of their ultimate adult size by 11 months, exhibiting faster growth rates than late developers (despite having similar adult size). Male cubs born into larger social groups tended to follow the late developer phenotype. Our results support the hypothesis that a minimum body size is required to reach sexual maturity, which may be achieved at different ages, even within a single population, where early maturity can confer individual fitness advantages and enhance population growth rate.
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- Linking plasma sex steroid hormone levels to the condition of external genitalia in European badgers (Meles meles): A critical evaluation of traditional field methodology
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Field biologists often rely on examination of external genitalia as a proxy for mammalian reproductive condition. In seasonally breeding European badgers, scrotal testes are used as an indicator of spermatogenesis, while a pink and swollen vulva with mucosal secretion is assumed to indicate oestrus. Systematic validation of these assumptions is lacking. Here we analysed sex steroid hormones from plasma samples collected from sexually mature adults during the winter mating season, the spring post-weaning period, the summer minor mating peak, and autumn reproductive quiescence, to compare circulating testosterone levels in males (n = 216), and oestrone (n = 143) and oestradiol (n = 36) levels in females with concurrent external genitalia condition (males: descended, intermediate, ascended testes, as well as testes volume; females: swollen, intermediate, normal vulva). Sex-steroid levels exhibited seasonal patterns, broadly reflecting the seasonal variation in genital condition. Nevertheless, on an individual level, male testosterone levels correlated significantly with testes condition and testes volume only during the mating season in spring, and neither oestrone nor oestradiol differed between female EGM categories. We thus conclude that, in males, EGM is a reliable indicator of reproductive activity during the mating season, but can provide only a tentative indication of physiological reproductive status outside this period, while in females EGM is generally less precise for assessing female reproductive status.
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- Encoded Information Within Urine Influences Behavioural Responses Among European Badgers (Meles meles)
- Description:
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Metabolic by-products like sex-steroid metabolites convey information regarding an individual’s physiological fitness and reproductive state. Urine and faeces containing these excreted metabolites can function as cues for conspecifics within social contexts, particularly for mate selection. Our pilot study investigated in scent provisioning experiments how donor- and responder-related characteristics influenced behavioural responses towards excreted sex-steroid metabolites. We used 51 urine samples with known urinary hormone concentrations (determined by EIA corrected for specific gravity) collected from known individuals in a high-density population of European badgers ( Meles meles ) in Wytham Woods, Oxfordshire, UK during the spring mating season. Samples were provided in Eppendorf tubes pushed into the ground near badger setts to assess how response likelihood, sniff duration, and countermarking responses varied according to donor-related traits (age, sex, group familiarity and hormone concentrations). From 143 videos containing 26 identifiable adult responders, we observed adult badgers modifying their behaviour towards urine samples based on the perceived relevance to their own traits with badgers investigating and countermarking urine from opposite-sex donors more often than urine from same-sex donors. This suggests that urine-marking can serve as an adaptive signal for individual advertisement. Additionally, all badgers were more likely to investigate male urine (containing testosterone) than female urine (containing oestradiol); however, no other clear effects of sex-steroid metabolites were noticed. We consider that this could be a feature of the social evolution of badgers or arise because badgers signal reproductive status through other olfactory secretions, notably their unique subcaudal gland marking behaviour.
- Related item:
- Extrinsic factors affecting cub development contribute to sexual size dimorphism in the European badger (Meles meles)
- Description:
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Sexual size dimorphism (SSD) is common among mammals, with males typically being larger than females, as a product of sex-specific differences in growth rate and growth duration. The Musteloidea, however, exhibit a hypo-allometric reduction in SSD with increasing body size (contrary to Rensch’s rule). A variety of extrinsic factors can affect juvenile growth rates and end body size, where one sex may demonstrate greater vulnerability than the other towards a specific factor, moderating patterns and degrees of SSD. Here, we analyse how male and female European badgers (Meles meles) differ in their somatic growth patterns. We compare the sex-specific growth curves across a range of somatic parameters and investigate what extrinsic (social and environmental) factors affect cub growth rates during the first 2 years of life leading to their sexual-dimorphic adult sizes. We found that average male final size of all measurements was significantly larger than those of females. Although male and female weanling cubs had similar body sizes, growth curves diverged significantly from ca. 11 months onwards due to continuous rapid growth of males versus slowing female growth. Consequently, females always concluded growth earlier than did males. In both sexes, extremities ceased to grow at an earlier age than did body length and zygomatic arch width. All badger cubs were impacted by their social environment as well as by weather conditions; however, male cubs were more sensitive to social factors, remaining smaller in social groups with more adult males present, whereas female final size was predominantly affected by weather and associated food availability. We discuss how extrinsic parameters can moderate patterns of SSD in the context of the differential equilibrium model.
