Different populations of the Antarctic notothen fish Trematomus scotti differ in key life history traits

Antarctic notothenioid fish form an adaptive radiation that diversified in the Southern Ocean over the past 10 million years. The biology and life history of about a third of notothenioids have been studied, however, most frequently from a single location. Because species distributions can be discontinuous and depend on environmental conditions, local populations might differ substantially both genetically and phenotypically from distant conspecifics. Among notothenioids, the 15 Trematomus species diversified to occupy environments ranging from subsurface cryopelagic habitats to the deep sea and many Trematomus species likely have circumpolar distributions. Here, we analyzed life history traits of the notothen Trematomus scotti from two distinct geographic areas: Andvord Bay, a fjord on the Western Antarctic Peninsula, and the Weddell Sea at the edge of pack ice zones. These two populations inhabit drastically different areas with important differences in environmental conditions driven by latitude, temperature and ice cover, thus enabling the study of the effects of the environment on life history traits. We first found no evidence for substantial genetic heterogeneity based on the mitochondrial marker mt-co1. Fish in Andvord Bay, however, grew faster and reached longer sizes than congeners in the Weddell Sea. Furthermore, females in Andvord Bay had higher fecundity but produced smaller eggs compared to females in the Weddell Sea. Thus, these two populations of T. scotti displayed distinct life histories likely in response to local environmental conditions. Local life history traits such as these are crucial to consider to evaluate the vulnerability of a species to environmental change.