Responses to desiccation vary among populations of an endemic freshwater isopod, Paramphisopus palustris

Abstract

Abstract Isopods play many important roles within freshwater ecosystems (including as shredders, prey, and detritivores), yet we know little about their responses to disturbance or whether they vary among populations. In a region undergoing severe climatic drying that is changing hydrological regimes in wetlands, we compared responses to drying (including survival) among populations of an endemic isopod Paramphisopus palustris (Amphisopidae). The survival of individuals from four isopod populations (two each from seasonal and semi‐perennial wetlands) were tested in a drying experiment with three treatments: control (permanently inundated), saturated sediment (water level maintained equal with the sediment surface), and dry (microcosms gradually raised out of the water causing sediments to dry out). Microrefuge use (three levels: no response, sought shelter or sought shelter/burrowed) was also compared among populations. As expected, isopod mortality was highest in the dry treatment for all populations. Unexpectedly, isopods from the two semi‐perennial wetlands showed higher survival in response to drying than those from seasonal wetlands. All isopods showed dormancy in response to the dry treatment and curled their bodies to limit water loss from their ventral gills. Microrefuge use differed among populations but not between the two hydroregimes. However, there was some similarity in population responses according to genetic clade. Isopods displayed some resistance to drying through dormancy behaviour and seeking microrefuges, which will increase population persistence under a drying climate. However, the reduced survival of individuals from seasonal wetland populations suggests that surviving in these wetlands is more challenging than in semi‐perennial or perennial regimes. These challenges are likely to be exacerbated as climate change further decreases hydroperiods and limits the availability of damp microrefuges. Consequently, longer‐term population persistence may be challenged as more wetlands become seasonal. The responses of endemic species are not always correctly predicted from knowledge of more widespread and commonly studied species and our results suggest that there may be variation among populations. Although P. palustris showed some innate responses to drying, their long‐term persistence (and that of other endemic species) may be threatened as environmental conditions become more extreme.