Data from: Patterns in antipredator armature reduction and maintenance in isolated spring populations of an amphipod crustacean

Organisms colonizing new habitat can undergo adaptive change due to novel
selective landscapes encountered in the new environment. Examples in
nature where development of the same traits has repeatedly occurred on
multiple independent occasions upon colonizing a novel habitat represent
instances of parallel evolution. Here we test whether the colonization of
spring habitat by the principally lacustrine amphipod crustacean
Pallaseopsis quadrispinosa has resulted in parallel evolution in armature
traits using empirical data on morphology and mitochondrial DNA and
through a breeding experiment. Analysis of mtDNA CO1 sequences shows that
the spring populations share no common history and have evolved in
isolation from each other and from their neighbouring lake populations
since deglaciation approximately 12000 years ago and are now fixed for
different haplogroups. Dorsal spines and lateral projections were absent
or less developed in all spring populations than in lake populations.
Variation in armature development also could be explained by predator
presence as populations with fish predators exhibited more developed
spines than those without fish. In a laboratory breeding experiment,
hybrid Spring X Lake F1 offspring had intermediate development of armature
when compared to offspring of Lake X Lake and Spring X Spring matings. The
results support the hypothesis that armature reduction has independently
evolved on multiple occasions in P. quadrispinosa. Recent research has
questioned the degree to which parallel evolution actually explains
variance in traits. Taking into account predation regime, sexual
dimorphism and mineral composition of the trait, a more precise
understanding of the factors influencing parallel evolution emerges.