Endocrine correlates of gender and throat coloration in the southern ground‐hornbill (Bucorvus leadbeateri)

Abstract

The southern ground‐hornbill (SGH) is a cooperatively breeding bird endemic to eastern and southern Africa, but is endangered in its southern distributional range. The national conservation restoration program harvests redundant chicks for captive breeding and reintroduction; with sexing and social grouping of the species evaluated by throat‐skin coloration, with adult males displaying a completely red color compared to dark blue within the red observed in adult females. However, recent findings indicate that dominant and subordinate adult males exhibit patches of blue throat‐skin. To optimize SGH management practices, it is vital to determine the role of red and blue coloration, as well as the possible drivers thereof. As a prerequisite, an enzyme immunoassay for monitoring fecal androgen metabolite (fAM) concentrations in SGH was established. Following this, fresh fecal samples were collected from 78 SGH, of various demographics and origin, across 12 captive institutions, to determine whether fAM concentrations differ between blue (B), partially blue (sB), and fully red (R) throat‐skin colored SGH. Furthermore, fAM concentrations were compared between males housed in different social groups of different age and sex classes. Individual median fAM concentrations of B, sB, and R adult males did not differ significantly but were considerably higher in B and sB males compared to R males. Social dynamics within captivity, for example, dominance, played no role as a driver of male gonadal activity or throat skin coloration. The results of the study indicate that androgens and apparent social dynamics are not primary determinants of throat coloration in male SGH.

Geographic Variation in Organ Size in a Toad (Duttaphrynus melanostictus)

“…Phenotypic plasticity, the ability of organisms to modify their morphological and physiological characteristics in response to diverse environmental conditions, which is important for the adaptation of species to different environmental conditions, is widely recognized across animal taxa [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. For example, the same genotype may exhibit distinct phenotypic traits as an adaptive mechanism in response to environmental fluctuations [ 20 , 21 ].…”

Geographical Variation in Body Size in the Asian Common Toad (Duttaphrynus melanostictus)

“…The environmental factors temperature and rainfall are two important selective forces that lead to geographic variation in morphological, physiological and life-history characteristics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Especially, temperature is a key factor that leads to geographic variation in age and body size in animals because the responses to environmental temperature along geographic gradients are likely influenced not only by energy storage but also by food intake [13,20,21].…”

Geographical Variation in Body Size and the Bergmann’s Rule in Andrew’s Toad (Bufo andrewsi)

“…Body size is a key life-history trait [ 33 , 34 , 35 , 36 , 37 ] that is affected by some factors, including resource consumption, interactions, population dynamics and community assembly in different environments [ 38 , 39 , 40 , 41 ]. Thus, body size should be associated with metabolic rate, population density, longevity, and geographic range (see [ 38 , 42 , 43 ]). Identifying the environmental factors that affect body size variation among populations is important in order to understand how animals adapt to abiotic environments by changing their phenotypic plasticity [ 22 , 44 , 45 , 46 , 47 , 48 ].…”