Open AccessSearching for constraints by cross‐species comparison: reaction norms for age and size at maturity in insects
Author(s) -
Tammaru Toomas,
Vellau Helen,
Esperk Toomas,
Teder Tiit
Publication year - 2015
Publication title -
biological journal of the linnean society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.906
H-Index - 112
eISSN - 1095-8312
pISSN - 0024-4066
DOI - 10.1111/bij.12417
Subject(s) - biology , instar , similarity (geometry) , larva , constraint (computer aided design) , lepidoptera genitalia , phylogenetic tree , evolutionary biology , maturity (psychological) , ecology , phylogenetic comparative methods , zoology , mathematics , genetics , artificial intelligence , psychology , developmental psychology , geometry , computer science , gene , image (mathematics)
An evolutionary explanation should consider the balance between environmentally‐based selective pressures, and the resistance of the organism's phenotype to adaptive evolution, with the latter being captured by the concept of constraint. The limited attention to non‐adaptive explanations in evolutionary ecology is at least partly caused by methodological difficulties with respect to identifying and quantifying constraints. As an example of an experimental approach evaluating a constraint‐based explanation, we present a cross‐species comparison of the shape of reaction norms for size and age at maturity. Instar‐ and sex‐specific development times and final sizes were recorded for two distantly‐related species of insects ( L epidoptera), with larval growth rates being manipulated by means of refined starvation treatments. We found that (1) the ‘classical’ L ‐shaped reaction norms for final size and development time are characteristic also of individual larval instars; (2) these responses show a high degree of quantitative similarity across the species, different larval instars, and sexes within species; and (3) the similarity among species and sexes is higher for the penultimate than for the final instar. The high degree of similarity suggests that some physiological mechanisms determining such reaction norms are evolutionarily conservative. An alternative explanation (i.e. quantitative similarity of ecologically based selective pressures) appears less likely. The results of a previous study on a third lepidopteran species not only support our general conclusions, but also provide a clear case of adaptive evolution in some aspects of such reaction norms. The present study shows one way how the data required to measure evolutionary conservatism in reaction norms for body size can be obtained empirically. © 2014 T he L innean S ociety of L ondon, B iological J ournal of the L innean S ociety , 2015, 114 , 296–307.