Evolutionary mechanisms of habitat invasions, using the copepodEurytemora affinisas a model system

Abstract

The study of the copepod Eurytemora affinis has provided unprecedented insights into mechanisms of invasive success. In this invited review, I summarize a subset of work from my laboratory to highlight key insights gained from studying E. affinis as a model system. Invasive species with brackish origins are overrepresented in freshwater habitats. The copepod E. affinis is an example of such a brackish invader, and has invaded freshwater habitats multiple times independently in recent years. These invasions were accompanied by the evolution of physiological tolerance and plasticity, increased body fluid regulation, and evolutionary shifts in ion transporter (V‐type H+ ATPase, Na+, K+‐ATPase) activity and expression. These evolutionary changes occurred in parallel across independent invasions in nature and in laboratory selection experiments. Selection appears to act on standing genetic variation during invasions, and maintenance of this variation is likely facilitated through ‘beneficial reversal of dominance’ in salinity tolerance across habitats. Expression of critical ion transporters is localized in newly discovered Crusalis leg organs. Increased freshwater tolerance is accompanied by costs to development time and greater requirements for food. High‐food concentration increases low‐salinity tolerance, allowing saline populations to invade freshwater habitats. Mechanisms observed here likely have relevance for other taxa undergoing fundamental niche expansions.

Invasions and extinctions through the looking glass of evolutionary ecology

“…In invasive species, rapid plasticity evolution can promote subsequent spread into new habitats. For instance, cane toads (Rhinella marina) that have spread to colder regions in Australia have evolved higher metabolic plasticity [101]; invasive freshwater populations of the marine-native copepod Eurytemora affinis have evolved increased ion-transport plasticity [96]; and a shrubby South African Senecio introduced into Spain has evolved greater reproductive output in wet conditions without any loss of fitness in its ancestral dry habitat [102].…”

Population genetics of two allopatric (North Sea and Baltic Sea) populations of Evadne nordmanni (Podonidae): Similarities and differences

“…If salinity is subject to constant fluctuation as in the south western Baltic Sea, the osmotic and ionic regulation gets increasingly challenging (Kultz, ). For example, food consumption by Eurytemora affinis has been shown to increase tremendously after transfer to freshwater conditions due to increased energy demand for osmoregulation (Lee, ). The exclusively Baltic branch of the haplotype network comprised mainly specimens sampled in the horohalinicum salinity range and from locations with salinities around it.…”

Population Genomics of Marine Zooplankton

“…Results can be interpreted to estimate and understand the age of the lineage in terms of time to coalescence (i.e., the common ancestral gene from which all current copies of the gene are descended), as well as imprints of demographic history on populations and species (Knowles 2009). Among marine zooplankton, mitochondrial markers have been used most regularly to infer demographic history (e.g., Peijnenburg et al 2005;Aarbakke et al 2014;Cornils et al 2017), including marine invasions (Cristescu 2015;Lee 2016;Sherman et al 2016), population expansions and contractions (Edmands 2001), geographic isolation giving rise to speciation events (Lee 2000;Peijnenburg et al 2004;Miyamoto et al 2010), and divergence of genetic lineages following major global climate events (Papadopoulos et al 2005;Blanco-Bercial et al 2011b;Milligan et al 2011). …”