Variation in testis weight of the Tibetan toad Scutiger boulengeri along a narrow altitudinal gradient

in Animal Biology
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Life-history theory predicts that organisms inhabiting harsh environments such as high altitudes should invest less in reproduction and more in survival. Testis size is associated with the intensity of male-male competition for mating and thus may be treated as an indicator of male reproductive investment. Hence, it may be expected that organisms will reduce their testis size with increasingly harsh environments. Here we test this prediction in a toad species, Scutiger boulengeri, endemic to the Tibetan plateau using data from three populations located at altitudes of 4078, 4276, and 4387 m. Consistent with the prediction, male toads exhibited smaller testes at higher altitudes, despite the relatively narrow altitudinal span. It is likely that cold climates and strong seasonality constrain the ability of high-altitude male toads to allocate more energy into reproduction, thereby leading to small testis size. In addition, the left testis was significantly heavier than the right one and the degree of size asymmetry was unrelated to either altitude or body condition.

Variation in testis weight of the Tibetan toad Scutiger boulengeri along a narrow altitudinal gradient

in Animal Biology



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    Mean annual temperature (A), and mean annual precipitation (B) in relation to altitude in southeastern Tibet (the regression lines were fit to data from the 1966-2016 database of the Tibet Meteorological Bureau). The altitudes at which the toads were sampled are: a, 4078 m; b, 4276 m; c, 4387 m.

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    Body length, body weight, age and testis weight of Scutiger boulengeri from three populations.

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    Resultsof GLMs that were fitted to investigate testis weight of Scutiger boulengeri from three populations in relation to altitude. Significant values are in italics.

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    Testis weight of Scutiger boulengeri from three populations, showing the predicted values from GLM models (mean ± SE). A. Left testis, B. Right testis, C. Both testes. Asterisks indicate a significant difference (P<0.05) between the groups.

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    Testis weight in relation to body weight of Scutiger boulengeri from three populations. The lines are the predicted values from GLMs. A. Left testis, B. Right testis, C. Both testes; a. 4078 m, b. 4276 m, c. 4387 m.


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