| DIFFERENTIAL RESPONSE OF GENOTYPES TO ALTERNATIVE ENVIRONMENTS: A COMPARATIVE MORPHOLOGICAL STUDY OF GALL-INDUCING APHIDS (HOMOPTERA: PEMPHIGIDAE: FORDINAE) |
ORA MANHEIM A1 and DAVID WOOL A1
A1 Department of Zoology, Tel Aviv University, Tel Aviv 69978, Israel
The dimensions of an adult insect's body parts reflect, in part, the conditions it was exposed to during the larval stages--be it nutrition, temperature, density, or other environmental constraints. Morphological differences between two genetically-similar adult morphs may reflect differences in their larval habitat. The life cycle of gall-inducing aphids (Homoptera: Pemphigidae: Fordinae) includes two winged (alate) adult morphs. The fall migrants develop in the closed galls on Pistacia and emerge as adults at the end of summer. The sexuparae develop on the roots of grasses in winter--without forming galls--and emerge as adults in the spring. The subfamily Fordinae is divided taxonomically into two tribes, Baizongiini and Fordini, which share the same life cycle. We measured 25 morphological characters on each of 156 fall migrants and 115 sexuparae, belonging to 11 species of Fordinae. We used cluster analysis to assess the morphological similarity of the species and morphs to each other. We employed conventional statistical techniques to compare the two morphs of each species, in light of the difference in larval environment of the morphs. We found, unexpectedly, that the two tribes within the Fordinae show contrasting levels of environmental control of morphology. In the Baizongiini, the sexuparae and the fall migrants of each species clustered together, implying similar morphology despite the difference in larval environment. This can be due to high heritability of the morphological characters. Not so in the Fordini: The sexuparae of all species clustered together and formed a separate cluster from the fall migrants. The sexuparae of different species are, most probably, genetically different, but experience a similar larval environment that is ecologically different from the gall environment of the fall migrants. The larval environment seems to have an overriding effect over any other factors--genetic or otherwise--controlling the expression of adult morphological characters in this tribe.
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