From local adaptation to ecological speciation in copepod populations from neighboring lakes

PLoS One. 2015 Apr 27;10(4):e0125524. doi: 10.1371/journal.pone.0125524. eCollection 2015.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Biological*
  • Animals
  • Copepoda / anatomy & histology
  • Copepoda / classification*
  • Copepoda / physiology*
  • DNA, Mitochondrial / analysis*
  • Evolution, Molecular
  • Female
  • Gene Flow
  • Genetic Fitness
  • Genetic Speciation
  • Lakes
  • Male
  • Mexico
  • Phenotype
  • Phylogeny
  • Population Dynamics
  • Reproductive Isolation*
  • Salinity

Substances

  • DNA, Mitochondrial

Grants and funding

This research was supported by Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica, Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México (PAPIIT IN-222709 and IN-217513; http://dgapa.unam.mx/html/papiit/papit.html) to JCP and EOM, Programa de Apoyo a los Profesores de Carrera para la Formación de Grupos de Investigación – FES Iztacala, UNAM (PAPCA 2007–2008; http://www.iztacala.unam.mx/spcc/spcc_papca.php) to EOM and JCP. OABM thanks the scholarship granted by Consejo Nacional de Ciencia y Tecnología (CONACYT; http://www.conacyt.mx/) to support his PhD research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.