From Local Adaptation to Ecological Speciation in Copepod Populations from Neighboring Lakes

Abstract

Continental copepods have been derived from several independent invasive events from the sea, but the subsequent evolutionary processes that account for the current diversity in lacustrine environments are virtually unknown. Salinity is highly variable among lakes and constitutes a source of divergent selection driving potential reproductive isolation. We studied four populations of the calanoid copepod Leptodiaptomus cf. sicilis inhabiting four neighboring lakes with a common history (since the Late Pleistocene) located in the Oriental Basin, Mexico; one lake is shallow and varies in salinity periodically (1.4–10 g L-1), while three are deep and permanent, with constant salinity (0.5, 1.1 and 6.5 g L-1, respectively). We hypothesized that (1) these populations belong to a different species than L. sicilis sensu stricto and (2) are experiencing ecologically based divergence due to salinity differences. We assessed morphological and molecular (mtDNA) COI variation, as well as fitness differences and tests of reproductive isolation. Although relationships of the Mexican populations with L. sicilis s.s. could not be elucidated, we identified a clear pattern of divergent selection driven by salinity conditions. The four populations can still be considered a single biological species (sexual recognition and hybridization are still possible in laboratory conditions), but they have diverged into at least three different phenotypes: two locally adapted, specialized in the lakes of constant salinity (saline vs. freshwater), and an intermediate generalist phenotype inhabiting the temporary lake with fluctuating salinity. The specialized phenotypes are poorly suited as migrants, so prezygotic isolation due to immigrant inviability is highly probable. This implication was supported by molecular evidence that showed restricted gene flow, persistence of founder events, and a pattern of allopatric fragmentation. This study showed how ecologically based divergent selection may explain diversification patterns in lacustrine copepods.

Absence of postmating barriers between a selfing vs. outcrossing Chilean Mimulus species pair

“…Similarly, postmating isolation is enhanced if hybrids are less well adapted than their parents to the available niches (Hatfield and Schluter, 1999). Ecological selection may be imposed by the abiotic environment (e.g., Barrera‐Moreno et al, 2015; Wogan and Richmond, 2015), or by features of the biotic environment such as predators and pollinators (e.g., Amico et al, 2007; Langerhans et al, 2007; Van der Niet et al, 2014). Because ecology and genetics are intimately intertwined in the process of speciation (and particularly sympatric speciation), it is useful to study speciation in taxonomic groups that are amenable to both fields of inquiry.…”

Phylogeography and genetic diversity of the copepod family Cyclopidae (Crustacea: Cyclopoida) from freshwater ecosystems of Southeast Nigeria

“…Additionally, four populations of Leptodiaptomus cf. sicilis in Mexico were found to diverge into 3 distinct phenotypes, and their specialization was further supported by molecular data which showed persistence of a founder effect, limited gene flow, and a pattern of allopatric speciation [40].…”

Population growth of microcrustaceans in water from habitats with differing salinities

“…A showed no differences. As a group, copepods are found in a multitude of environments, lakes, salt marshes, shorelines and many more habitats ( Coull et al, 1979 ; Lee, Remfert & Gelembiuk, 2003 ; Barrera-Moreno et al, 2015 ). They also have a history of invading freshwater environments from a saltier home environment ( Lee, 1999 ; Lee, Remfert & Gelembiuk, 2003 ) due to their ability to adapt to their local environment’s salinity.…”