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.