Evol Ecol Res 9: 1305-1318 (2007)     Full PDF if your library subscribes.

Fitness benefits of diverse offspring in pygmy grasshoppers

Anders Forsman,* Jonas Ahnesjö and Sofia Caesar

School of Pure and Applied Natural Sciences, University of Kalmar, SE-391 82 Kalmar, Sweden

Author to whom all correspondence should be addressed.
e-mail: anders.forsman@hik.se


Question: Do females obtain fitness benefits from an increase in offspring diversity?

Hypotheses: Polyandry increases offspring diversity within a clutch. Increased offspring diversity will reduce competition among siblings (manifested as increased mean survival in more diverse families) and the probability that all offspring might be ill-suited to future conditions (manifested as lower variance in survival in diverse families).

Organisms: Pygmy grasshoppers, Tetrix subulata and Tetrix undulata, that are polymorphic for colour pattern.

Field site: South-central Sweden.

Methods: We varied the number of mates provided to colour polymorphic pygmy grasshoppers. We reared families in either warm or cold conditions using a split-brood design.

Conclusions: The colour morph diversity of broods increased with the number of experimentally provided mates. Colour morphs represent alternative strategies that differ in body size, physiology, behaviour, and life history. Survival increased with increasing sibling diversity, supporting the hypothesis that different morphs avoid competition by using different subsets of available resources. Homogeneous families (in which all siblings belong to the same or only a few colour morphs) varied more in survival than did families with diverse siblings, supporting the hypothesis that morphs vary in their ability to cope with and utilize different resources.

Keywords: colour polymorphism, offspring diversification, polyandry, selective free-rider.

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