Does testis weight decline towards the Subarctic? A case study on the common frog, Rana temporaria

Abstract

Interpopulation comparisons of variation in resource availability and in allocation patterns along altitudinal and latitudinal gradients allow insights into the mechanisms shaping the life history of animals. Patterns of between-population differences in female life history traits have been studied intensively across a wide range of taxa, but similar investigations in males have remained scarce. To study if testis weight-a measure of reproductive investment-varies on a geographical scale in anurans, we focussed on the variation in relative testis weight (RelTW) and asymmetry in 22 populations of the common frog Rana temporaria along a 1,600-km latitudinal transect across the Scandinavian peninsula. We found that RelTW decreased towards the north. Body mass and body length both had independent positive effects on testes mass. We found evidence for directional asymmetry (DA) in testis weight with the right testis being larger than the left. The level of DA in testis weight was not related to latitude, but both body mass and testes mass had independent positive effects on asymmetry. We discuss the northwards decrease in RelTW in terms of a decreased reproductive investment as a possible consequence of harsher environmental conditions, and perhaps also, weaker sexual selection in the north than in the south.

The genetic contribution to sex determination and number of sex chromosomes vary among populations of common frogs (Rana temporaria)

“…DNA extractions were performed using a silica-based method as described in Ivanova et al (2006). Phenotypic sex of wild-caught frogs was identified on the basis of secondary sexual traits (that is, white throat and presence of nuptial pads in males and red coloration and presence of eggs in females) and later confirmed by dissection for the purpose of other studies (Hettyey et al, 2005;Hjernquist et al, 2012).…”

Responses in the diet composition of the Common frog (Rana temporaria) to the stochastic gradation of Autumnal moth (Epirrita autumnata) larvae

“…Slow growth must be a combined result of the short activity season (short time window to acquire energy for growth, overwintering and reproduction) and the increased need for energy storage important to buffer against climatic stochasticity (JÖnsson et al 2009). These energetic constraints are strong enough to negatively affect reproductive investments, which are of central importance in increasing individual fitness (Hettyey et al 2005). Such extreme energy constraints will force frogs to utilize any possible prey item they encounter, and thus indeed pose strong selection for a generalist opportunistic foraging strategy, especially because densities of many potential prey species tend to decrease towards high latitudes (Brown 1984, Barrios-Garcia et al 2015, Kozlov et al 2015.…”

Distributional range, ecology, and mating system of the Cape mole-rat (Georychus capensis) family Bathyergidae

“…Similar allometry applied to testicular mass, which relied significantly on male body mass (also see Merilä and Sheldon 1998;Jolly and Phillips-Conroy 2001;Hettyey et al 2005 for similar examples in other taxa). In addition, the body condition index of males also has a slight effect on testicular mass, however it seems that testicular growth is, to a larger extent, an allometric function of an individual's size than of its body condition.…”

“…Testicular mass was regressed against male body mass and the residuals of this relationship calculated to obtain relative testicular mass (a widely used measure of male reproductive investment; Hettyey et al 2005) using a linear regression. This analysis was performed including only adult males (all males weighing less than 120g were removed) from populations with sample sizes of more than 3 specimens (i.e., small populations were removed).…”

“…In addition, sperm competition (Merilä and Sheldon 1998;Jolly and Phillips-Conroy 2001;Preston et al 2002;SchulteHostedde and Millar 2004;Hettyey and Roberts 2006), scramble competition polygyny (Clutton-Brock 1989;Davies 1991), the temporal and spatial distribution of the sexes (Davies 1991;Reynolds 1996) and the operational sex ratio of a species (Greenwood 1980;Hettyey and Roberts 2006) are also influential in determining intraspecific variation in reproductive biology. Such intraspecific geographic variation has been demonstrated in litter size (Hill 1972;Waltner 1991;Mathies and Andrews 1995;Rohr 1997;Lemos-Espinal et al 1998) and testicular size (Merilä and Sheldon 1998;Hettyey et al 2005) due to various ecological and biological factors.…”