The competition for fertilization among sperm from different males can drive variation in male reproductive investments. However, the mechanisms shaping reproductive allocation and the resulting variations in reproductive investment relative to environmental variables such as resource availability and male-male competition remain poorly known in frogs. Here, we investigated inter-population variation in male somatic condition and testis mass across four populations of the swelled vent frog Feirana quadranus along an altitudinal gradient. We found that relative testis mass did not increase with altitude, which was inconsistent with previous predictions that an increase in latitude and/or altitude should result in decreased sperm production in anurans due to shortened breeding seasons and the decline in resource availability. We also found no increase in somatic condition and male/female operational sex ratio with altitude. However, the somatic condition exhibited a positive correlation with testis mass, which indicated the condition-dependent testis size in F. quadranus. Moreover, an increase of testis mass with increasing male/female operational sex ratio suggest that male-male competition can result in an increased intensity of sperm competition, thereby increasing testis mass.
BuzattoB.A.ThyerE.M.RobertsJ.D. & SimmonsL.W. (2017) Sperm competition and the evolution of precopulatory weapons: testis size and amplexus position, but not arm strength, affect fertilization success in a chorusing frog. Evolution71329-341.
BuzattoB.A.RobertsJ.D. & SimmonsL.W. (2015) Sperm competition and the evolution of precopulatory weapons: increasing male density promotes sperm competition and reduces selection on arm strength in a chorusing frog. Evolution692613-2624.
ChenM.HuangY.LiuG.QinF.YangS. & XuX. (2016a) Effects of enhanced UV-B radiation on morphology, physiology, biomass, leaf anatomy and ultrastructure in male and female mulberry (Morus alba) saplings. Environ. Exp. Bot.12985-93.
HettyeyA. & RobertsJ.D. (2006) Sperm traits of the quacking frog, Crinia georgiana: intra- and interpopulation variation in a species with a high risk of sperm competition. Behav. Ecol. Sociobiol.59389-396.
HjernquistM.B.SödermanF.JönssonK.I.HerczegG.LaurilaA. & MeriläJ. (2012) Seasonality determines patterns of growth and age structure over a geographic gradient in an ectothermic vertebrate. Oecologia170641-649.
JinL.YangS.N.LiaoW.B. & LüpoldS. (2016b) Altitude underlies variation in the mating system, somatic condition and investment in reproductive traits in male Asian grass frogs (Fejervarya limnocharis). Behav. Ecol. Sociobiol.701197-1208.
KusanoT.TodaM. & FukuyamaK. (1991) Testes size and breeding systems in Japanese anurans with special reference to large testes in the treefrog, Rhacophorus arboreus (Amphibia: Rhacophoridae). Behav. Ecol. Sociobiol.2927-31.
MaiC.L.LiaoJ.ZhaoL.LiuS.M. & LiaoW.B. (2017a) Brain size evolution in the frog Fejervarya limnocharis does neither support the cognitive buffer nor the expensive brain framework hypothesis. J. Zool.30263-72.
McDonaldG.C.SpurginL.G.FairfieldE.A.RichardsonD.S. & PizzariT. (2017) Pre- and postcopulatory sexual selection favor aggressive, young males in polyandrous groups of red jungle fowl. Evolution711653-1669.
PascoalS.MendrokM.WilsonA.J.HuntJ. & BaileyN.W. (2017) Sexual selection and population divergence II. Divergence in different sexual traits and signal modalities in field crickets (Teleogryllus oceanicus). Evolution711614-1626.
Schulte-HosteddeA.I. & MillarJ.S. (2004) Intraspecific variation of testis size and sperm length in the yellow-pine chipmunk (Tamias amoenus): implications for sperm competition and reproductive success. Behav. Ecol. Sociobiol.55272-277.