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ARE PARALLEL MORPHOLOGIES OF CAVE ORGANISMS THE RESULT OF SIMILAR SELECTION PRESSURES?

Ross Jones1, David C Culver2, Thomas C Kane3

  • 1Department of Biology, Memorial University of Newfoundland, St. John's, NF, A1B 3X9, CANADA.

Evolution; International Journal of Organic Evolution
|June 1, 2017
PubMed
Summary

Selection drives parallel evolution in Gammarus minus, with smaller eyes in caves and larger eyes in springs. Cave populations show selection for larger body and antennae size, but spring populations exhibit unexpected selection for larger size.

Keywords:
CavesGammarus minusmorphologyregressive evolutionselectionsprings

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Area of Science:

  • Evolutionary Biology
  • Ecology
  • Speciation

Background:

  • Cave populations of Gammarus minus display distinct traits (larger size, longer antennae, smaller eyes) compared to spring populations.
  • Previous research indicates cave populations originated from independent colonization events in isolated subterranean systems, with existing genetic variation for these traits.
  • The study investigates whether parallel selection patterns in isolated cave environments contribute to the convergent evolution of cave-specific morphologies.

Purpose of the Study:

  • To test the hypothesis that parallel selection pressures in isolated cave populations drive the evolution of cave morphologies.
  • To examine directional selection on eye size, antennal length, and body size in both cave and spring populations of Gammarus minus.
  • To compare selection patterns between cave and spring environments and their consistency with observed phenotypic divergence.

Main Methods:

  • Utilized seasonal cross-sectional sampling of Gammarus minus populations from cave and spring habitats.
  • Assessed directional selection by analyzing variation in mating success and fecundity related to specific morphological traits.
  • Quantified selection gradients for eye size, antennal length, and body size in the sampled populations.

Main Results:

  • Confirmed significant directional selection for reduced eye size in cave populations and enlarged eye size in spring populations.
  • Observed selection favoring larger body and antennal size in cave populations, aligning with the parallel evolution hypothesis.
  • Detected selection for increased body and antennal size in spring populations, which contradicts the observed divergence between spring and cave forms.

Conclusions:

  • Selection is a key driver for reduced eye size in cave-dwelling amphipods and enlarged eyes in spring populations.
  • Parallel selection patterns in caves likely explain the observed elaboration of body and antennal size.
  • The unexpected selection for larger size in springs suggests unmeasured viability selection may counteract these pressures, warranting further investigation.