Testis Size Variation and Its Environmental Correlates in Andrew’s Toad (Bufo andrewsi)

Abstract

Reproductive investments influenced by environmental conditions vary extensively among geographically distinct populations. However, investigations of patterns of intraspecific variation in male reproductive investments and the mechanisms shaping this variation in anurans remain scarce. Here, we focused on the variation in testis size in 14 populations of the Andrew’s toad Bufo andrewsi, a species with weak dispersal ability but wide distribution in southwestern China, to establish whether male reproductive investment varies on an environmental gradient. Our analysis revealed a significant variation in relative testis size across populations, and a positive correlation between testis size and body condition. We, however, found no geographic trends explaining the variability in the testis size. The relative testis size did not increase with increasing latitude or altitude. We also found no relationship between relative testis size and rainfall, but a negative correlation with the coefficient of variation of temperature, with larger testes under stable environments. These findings suggest that the decreased male reproductive investment of this species may be a consequence of harsher or fluctuating environmental conditions.

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

“…To explore geographical variation in age structure (i.e., age at sexual maturity, longevity, and mean age) among the 14 populations, we first used the R package ‘lme4′ [ 94 , 104 ] to implement the generalized linear mixed models (GLMMs) with age as the dependent variable, sex as a fixed factor, and the population as a random factor. We then conducted GLMMs with age as the dependent variable, altitude and latitude as fixed factors, and population as a random factor to examine the effect of geographical gradients on age.…”

“…The Andrew’s toad ( Bufo andrewsi ) is not endemic to China and is widely distributed in the Hengduan Mountains, China, with altitudes ranging from 750 m to 3500 m [ 24 , 89 ]. Previous studies have investigated the life-history traits, male mating choice, testes mass, organ size (e.g., heart, lung, gallbladder, livers, spleen, kidneys, and digestive tract), and population genetic structure of this species [ 24 , 45 , 90 , 91 , 92 , 93 , 94 , 95 , 96 ]. However, studies on body size variation have investigated only a few populations [ 22 , 45 ].…”

Sexual Dimorphism in the Limb Bones of Asiatic Toad (Bufo gargarizans) in Relation to Sexual Selection

“…Previous studies found that the relative or absolute weight of males’ forelimb muscles associated with amplexus and hindlimb muscles, which are related to the scramble competition, are larger than that of females; however, the weight of the forelimb muscles, which is unrelated to the clasping action, does not differ between sexes [ 12 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. According to the sexual selection theory, such secondary sexual dimorphism in limbs is attributed to adaptation for amplexus, which is a behavior used in male–male competition [ 15 , 21 , 22 ]. However, bones are the attachment of muscles and the lever of movement, and knowledge on the differences in limb bone anatomy between the sexes is lacking [ 12 , 23 ].…”

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].…”