Geographic variation of reproductive tactics in lubber grasshoppers.

We investigate plastic and interpopulation variation of trade-offs among reproductive tactics. There is a potential three-way trade-off among timing of reproduction, somatic storage, and investment in reproduction. We tested whether this trade-off shows latitudinal interpopulation variation. We studied populations of the lubber grasshopper, Romalea microptera, from Florida (FL; lowest latitude), Louisiana (LA; intermediate latitude), and Georgia (GA; highest latitude), each tested at three diet levels. All three populations differed in their multivariate responses of the three reproductive tactics we studied. This difference across populations was due primarily to age at first reproduction, secondarily to somatic storage, and less so to clutch mass. Age at first reproduction was least in GA, intermediate in LA, and greatest in FL grasshoppers. Somatic storage was greatest in FL and LA, and least in GA grasshoppers. Clutch mass was greatest in LA and GA, and least in FL grasshoppers. Diet levels also differed in this suite of reproductive tactics, primarily due to variation in age at reproduction. In contrast to significant, independent effects of population and diet, we find no evidence that the trade-off itself varies across populations (as indicated by the non-significant interaction of population and diet level). Thus, we show that the innate allocation of resources among reproductive tactics is different across populations, but all three populations responded similarly to a range of diet levels.

Interpopulation variation in developmental titers of vitellogenin, but not storage proteins, in lubber grasshoppers.

We examined simultaneous plastic and latitudinal interpopulation variation in the time course of hemolymph protein titers during egg production in the lubber grasshopper. Our goal was to gain insight into possible evolutionary changes in the physiology underlying reproductive plasticity. We used lubbers from three locations in the United States (Florida [FL], Louisiana [LA], and Georgia [GA]), each offered three daily food rations. Previous genetic analysis indicated that grasshoppers from FL (the low-latitude population) and GA (the high-latitude population) were phylogenetically closer to each other than to LA grasshoppers (the intermediate-latitude population). The ages at maximum titers of vitellogenin (Vg(max)) and three storage proteins that were referred to as major hemolymph proteins (MHP(max)) were used as indices of the progress of oocyte development. Age at Vg(max) was affected significantly both by diet and by population. Perhaps most importantly, age at Vg(max) was less for GA grasshoppers than for FL and LA grasshoppers; this pattern differs from the phylogenetic relationships of the populations. Age at MHP(max) was significantly affected only by diet and not by population. Hence, the regulation of these proteins may differ across populations. Finally, we found no evidence that plasticity of reproductive investment in response to food availability differs across populations (as indicated by nonsignificant interactions of population and feeding environment).