Data from: Fitness and morphological outcomes of many generations of hybridization in the copepod Tigriopus californicus

Hybridization between genetically divergent populations is an important
evolutionary process, with an outcome that is difficult to predict. We
used controlled crosses and freely mating hybrid swarms, followed for up
to 30 generations, to examine the morphological and fitness consequences
of interpopulation hybridization in the copepod Tigriopus californicus.
Patterns of fitness in two generations of controlled crosses were partly
predictive of long-term trajectories in hybrid swarms. For one pair of
populations, controlled crosses revealed neutral or beneficial effects of
hybridization, and hybrid swarm fitness always equalled or exceeded that
of the midparent. For a second pair, controlled crosses showed F2 hybrid
breakdown, but elevated fitness in backcrosses, and hybrid swarm fitness
deviated both above and below that of the parentals. Nevertheless,
individual swarm replicates exhibited divergent fitness trajectories over
time that were not related in a simple manner to their hybrid genetic
composition, and fixation of fitter hybrid phenotypes was not observed.
Hybridization did not generally increase overall morphological variation,
and underlying genetic changes may have been masked by phenotypic
plasticity. Nevertheless, one type of hybrid swarm exhibited a repeatable
pattern of transgressively large eggsacs, suggesting a positive effect of
hybridization on individual fecundity. Additionally both parental and
hybrid swarms exhibited common phenotypic trends over time, indicating
common selective pressures in the laboratory environment. Our results
suggest that, in a system where much work has focused on F2 hybrid
breakdown, the long-term fitness consequences of interpopulation
hybridization are surprisingly benign.