Evol Ecol Res 15: 557-566 (2013)     Full PDF if your library subscribes.

Sexual selection on locomotor performance in the calanoid copepod Tigriopus californicus

Roberto F. Nespolo, Rodrigo A. Scheihing† and Paulina Artacho

Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile, Valdivia, Chile

Correspondence: R.F. Nespolo, Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile, Campus Isla Teja, Valdivia 5090000, Chile.
e-mail: robertonespolorossi@gmail.com


Background: A close association between locomotor performance, sexual selection, and fitness has been shown in many species, indicating that reproductive success depends on a complex interaction between locomotor efficiency and mating. Frequently, this interaction produces trade-offs between traits or sexes.

Aims: First, determine whether fitness (fecundity) maximization is traded off with locomotor performance in the context of mating and morphology in Tigriopus californicus, a small swimming crustacean. Second, identify if differences occur using different fitness surrogates (egg and offspring production).

Methods: In 110 males and females, we measured egg and offspring production per female, and a suite of attributes: swimming speed, body size (total length), and body elongation (body length/width). We computed trait repeatability of swimming speed and fitness surfaces using cubic splines and selected the best model using stepwise and AIC criteria.

Results: We found contrasting results using egg production versus offspring production as a fitness surrogate. Using egg production, the only target of selection was female size and subtle effects such as stabilizing and correlated selection were detected later, after measuring offspring production. Directional selection suggested that larger and faster males are more efficient in capturing females. Correlational selection between morphological attributes suggested that selection promotes opposite values of elongation and body size in females, and synergic combinations of elongation and body size in males.

Conclusions: Egg fecundity as a fitness surrogate could be misleading, as many effects could appear in a later life stage. Sexual selection on locomotor (swimming) performance appears to be important in copepods, because the criterion of fitness maximization differs in males and females. Correlational selection on morphological attributes also differed between sexes and between attributes (within sexes), suggesting several trade-offs.

Keywords: copepods, correlational selection, fitness, locomotor performance.

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