Diet-Induced Plasticity of Linear Static Allometry Is Not So Simple for Grasshoppers: Genotype-Environment Interaction in Ontogeny Is Masked by Convergent Growth.

Grasshoppers, Melanoplus sanguinipes (Orthoptera: Acrididae), develop larger head width (HW) and shorter leg length, relative to body size, when fed low nutrient, lignin-rich grasses compared to sibs fed a diet of high nutrient grasses. To elucidate how underlying genetic variation and plasticity of growth generate plasticity of this linear static allometry within coarse-grained environments, I measured head and leg size of three nymphal instars and adult grasshoppers raised on either a low or high nutrient diet within a half-sib quantitative genetic experiment. Doubly-multivariate repeated measures multiple analysis of variance (MANOVA) of head, mandible, and hind leg size and their rate of growth (mm/period) and growth period (days) through ontogeny were used to analyze how the ontogeny of diet-induced plasticity for these variables and additive genetic variation for plasticity (genotype × environment interaction [G×E]) contribute to plasticity in functional linear static allometry. Genetic variation for diet-induced plasticity (G×E) of head and leg size varied through ontogeny, as did genetic variation for plasticity of growth in third and fourth instar nymphs. Despite extensive genetic variation in plasticity of HW and leg length in fourth instar nymphs, the static allometry between head and leg was stable within each diet because the patterns of G×E were similar for HW, leg length and their coordinated growth. Nutrient sensitive plasticity in growth shifted the intercept but not the slope of static allometry, a result consistent with one outcome of a graphical model of the relationships between G× E and plasticity of within environment static allometry. In addition, G×E of fourth instar head and leg size was reduced in adults by negatively size-dependent, convergent growth in the last period of ontogeny. Consequently, the bivariate reaction norms of head and leg size for adults exhibited no G×E and, again, plasticity in the intercept but not in the slope of static allometry. The ontogeny of seemingly simple diet-induced linear static allometry between functional body parts in grasshoppers arises from a complex combination of differing patterns of nutrient-sensitive growth, duration of growth, convergent growth, and G×E, all relevant to understanding the development and evolution of functional allometry in hemimetabolous insects.

Sediment microbial communities in Great Boiling Spring are controlled by temperature and distinct from water communities.

Great Boiling Spring is a large, circumneutral, geothermal spring in the US Great Basin. Twelve samples were collected from water and four different sediment sites on four different dates. Microbial community composition and diversity were assessed by PCR amplification of a portion of the small subunit rRNA gene using a universal primer set followed by pyrosequencing of the V8 region. Analysis of 164 178 quality-filtered pyrotags clearly distinguished sediment and water microbial communities. Water communities were extremely uneven and dominated by the bacterium Thermocrinis. Sediment microbial communities grouped according to temperature and sampling location, with a strong, negative, linear relationship between temperature and richness at all taxonomic levels. Two sediment locations, Site A (87-80 °C) and Site B (79 °C), were predominantly composed of single phylotypes of the bacterial lineage GAL35 (\[pmacr]=36.1%), Aeropyrum (\[pmacr]=16.6%), the archaeal lineage pSL4 (\[pmacr]=15.9%), the archaeal lineage NAG1 (\[pmacr]=10.6%) and Thermocrinis (\[pmacr]=7.6%). The ammonia-oxidizing archaeon 'Candidatus Nitrosocaldus' was relatively abundant in all sediment samples <82 °C (\[pmacr]=9.51%), delineating the upper temperature limit for chemolithotrophic ammonia oxidation in this spring. This study underscores the distinctness of water and sediment communities in GBS and the importance of temperature in driving microbial diversity, composition and, ultimately, the functioning of biogeochemical cycles.

Consumption rates and the evolution of diet-induced plasticity in the head morphology of Melanoplus femurrubrum (Orthoptera: Acrididae).

Phenotypic plasticity may be an ecologically important evolutionary response to natural selection in multiple environments. I have determined the effect of diet-induced developmental plasticity in the head size of grasshoppers (Melanoplus femurrubrum) onfeeding performance on two types of plants. Full-sib families were divided and raised on either red clover, Trifolium repens, or rye grass, Lolium perenne. In three different stages of ontogeny, grasshoppers raised on rye grass had significantly larger heads, relative to body size, than full-sibs raised on clover. A principal components analysis indicated that two to five relative head size characters covaried as a block in their plastic response to the feeding environment. Regressions of adjusted consumption rates (mg/sec) against relative head size revealed that larger head sizes, induced by the rye grass diet, enhanced consumption rates of rye grass, but not clover. Unexpectedly, a similar positive association was observed between head size and consumption rate for grasshoppers raised on clover when they were feeding on clover. These results support the inference that grasshoppers exhibit adaptive phenotypic plasticity. However, the unexpected influence of head size on consumption rates of clover indicates that the functional relationship between head morphology and feeding performance is complex and that variation in this relationship among plant environments is not sufficient to explain the evolution of diet-induced phenotypic plasticity.

DIFFERENT SPATIAL SCALES OF ADAPTATION IN THE CLIMBING BEHAVIOR OF PEROMYSCUS MANICULATUS: GEOGRAPHIC VARIATION, NATURAL SELECTION, AND GENE FLOW.

Patterns of geographic variation in tree-climbing ability of Peromyscus maniculatus were used to examine the influence of spatial variation in natural selection and gene flow on the genetic divergence of climbing behavior among populations. Offspring of adults of two subspecies sampled from 10 localities in montane conifer forest, conifer woodland, and desert scrub/grassland habitats were raised in the laboratory and tested to determine their tree-climbing ability (the maximum diameter artificial rod that a mouse could climb). Comparisons of mean rod-climbing scores revealed that individuals of P. m. rufinus sampled from montane conifer forest and conifer woodland in Arizona were better climbers than P. m. sonoriensis sampled from conifer woodland and desert habitats in Nevada. This result was consistent with the hypothesis that natural selection has produced large-scale adaptation in climbing behavior. However, the climbing ability of P. m. sonoriensis sampled from conifer woodland habitats on isolated mountaintops in Nevada has not evolved in response to natural selection to the degree expected. In addition, populations sampled from desert grassland habitat, adjacent to woodland P. m. rufinus in Arizona, have climbing abilities that are not significantly different from conifer woodland populations. These observations indicate that local adaptation was constrained. An estimate of the heritability of climbing ability (h2 = 0.352 ± 0.077) indicates that lack of a response to selection was not due to the absence of additive genetic variation. In addition, regressions of interpopulation differences on the degree of geographic isolation between pairs of populations do not support the hypothesis that gene flow between habitats has constrained evolution. Instead, a combination of historical events and insufficient time to respond to selection appears to have influenced geographic variation and the spatial scale of adaptation in climbing ability.