The coadaptation of female morphology and offspring size: a comparative analysis in crickets |
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Authors: | Y Carrière S Masaki D A Roff |
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Institution: | (1) Department of Biology, McGill University, 1205 Dr. Penfield ave., Montreal, PQ, Canada, H3A 1B1, CA;(2) 12–13 Matsubara-Higashi 1, Hirosaki 036, Japan, JP |
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Abstract: | Few studies of invertebrates have considered combinations of morphological and life history traits in the context of the
evolution of reproductive strategies. Cricket species that exploit habitats harsh with respect to egg survival have evolved
a long ovipositor, presumably because laying deep in the soil reduces egg mortality. Yet hatchling mortality increases with
laying depth, and the ability of hatchlings to climb through the soil increases with egg size. Thus a conflict may exist between
survival of the egg and that of the hatchling, inducing a positive covariation between egg size and ovipositor length across
species evolving under contrasting selective habitats. We used the phylogenetic autocorrelation method and a path analysis
to assess whether egg size coevolved with ovipositor length across 40 species of crickets, and whether egg size was affected
by body size or ecological factors that influence egg mortality. Body size and ovipositor length were affected by taxonomic
association, whereas common ancestry had no significant effect on egg size, diapausing strategy, and oviposition preference
for soil types. The path model indicated that 29.11% of the variance in egg size was explained by independent evolution. As
expected, ovipositor length was positively correlated with egg size, and species diapausing in the egg stage produced larger
eggs than crickets diapausing in the nymphal stage or with no diapause. Ovipositor length and diapausing strategy were the
first and second most important traits, respectively, in term of the proportion of variance in egg size explained by specific
values. These results support the hypothesis that the ability of hatchlings to climb through the soil, and variation in diapause
strategies, are general selective factors affecting the evolution of egg size in crickets. Phylogeny explained 51.01% of the
variance in egg size. Egg size in a current cricket species, however, was not directly determined by egg size in its ancestor.
Instead, it was strongly related to the phylogenetic values of body size and ovipositor length. Such indirect phylogenetic
effects of body size and ovipositor length may have arisen because clades originating from ancestors with different ovipositor
lengths experienced different selective pressures on egg size.
Recelived: 13 October 1995 / Accepted: 30 September 1996 |
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Keywords: | Diapause Egg size Ovipositor length Oviposition behavior Crickets |
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