Altitudinal variation in male reproductive investment in a polyandrous frog species (Hyla gongshanensis jingdongensis).

Competition for fertilization in multi-male group spawning can drive variation in male reproductive investment (i.e., testis mass and sperm size). Inter-population comparisons of variation in energetic availability and allocation along geographical gradients allow insights into the mechanisms shaping the reproductive investments of animals. Although inter-population differences in female reproductive investment (i.e., clutch size and egg size) have been studied extensively across a wide range of taxa, little information on variation in reproductive investment in males is available. Here, we studied altitudinal variation in testis mass and sperm length among three populations in the Jingdong tree frog (Hyla gongshanensis jingdongensis), a polyandrous species, in Yunnan Province in China. The results showed that individuals exhibited smaller testes at higher altitudes while testes mass was positively correlated with body size, body condition and age. Longer sperm length was observed in the middlealtitude population. Moreover, we found that sperm number was positively correlated with testes mass and sperm length. Our correlational findings suggest that environmental constraints at high altitude select for less investment in testes and offspring number. [ABSTRACT FROM AUTHOR]