Dissecting the variance-covariance structure in insect physiology: the multivariate association between metabolism and morphology in the nymphs of the sand cricket (Gryllus firmus)

Energy metabolism in animals has been largely studied in relation to exogenous sources of variation. However, because they give insight into the relationship between whole metabolism and lower organizational levels such as organs and tissues, examination of endogenous determinants of metabolism other than body mass is itself very important. We studied the multivariate association of body parts and several aspects of energy metabolism in an insect, the nymphs of the sand cricket, Gryllus firmus. By using a variety of both univariate and multivariate techniques, we explored the resultant variance-covariance matrix to build a path diagram with latent variables. After controlling for body mass, we found a significant canonical correlation between metabolism and morphology. According to the factor loadings and path coefficients, the most important contributions of morphology to the correlation were thorax and abdomen size measures, whereas the most important metabolic contribution was resting metabolism. Activity metabolism was mostly explained by body mass rather than body parts, which could be a result of resting rates being chronic consequences of the functioning of the metabolic machinery that the insect must maintain.     

The evolution of fledging age in songbirds

In birds with altricial young an important stage in the life history is the age at fledging. In this paper we use an approach proven successful in the prediction of the optimal age at maturity in fish and reptiles to predict the optimal age of fledging in passerines. Integrating the effects of growth on future fecundity and survival leads to the prediction that the optimal age at fledging is given by a function that comprises survival to maturity, the exponent of the fecundity-body size relationship and nestling growth. Growth is described by the logistic equation with parameters, A, K and t(i). Assuming that the transitional mortality curve can be approximated by the nestling mortality, M(n), the optimal fledging age, t(f), is given by a simple formula involving the three growth parameters, nestling mortality (M(n)) and the exponent (d) of the fecundity-body size relationship. Predictions of this equation underestimate the true values by 11-16%, which is expected as a consequence of the transitional mortality function approximation. A transitional mortality function in which mortality is approximately 0.3-0.4 of nesting mortality (i.e. mortality declines rapidly after fledging) produces predictions which, on average, equal the observed values. Data are presented showing that mortality does indeed decline rapidly upon fledging.     

The costs of being dark: the genetic basis of melanism and its association with fitness‐related traits in the sand cricket

Melanism is an important component of insect cuticle and serves numerous functions that enhance fitness. Despite its importance, there is little information on its genetic basis or its phenotypic and genetic correlation with fitness‐related traits. Here, we examine the heritability of melanism in the wing dimorphic sand cricket and determine its phenotypic and genetic correlation with wing morphology, gonad mass and size of the dorso‐longitudinal muscles (the principle flight muscles). Previously demonstrated trade‐offs among these traits are significant factors in the evolution of life history variation. Using path analysis, we show that melanization is causally related to gonad mass, but not flight muscle mass. Averaged over the sexes, the heritability of melanism was 0.61, the genetic correlation with gonad mass was ?0.36 and with wing morph was 0.51. The path model correctly predicted the ranking of melanization score in lines selected for increased ovary mass, increased flight muscle mass, an index that increased both traits and an unselected control. Our results support the general hypothesis that melanization is costly for insects and negatively impacts investment in early reproduction.     

Alternative strategies: the evolution of switch points

The evolution of conditional, alternative strategies is a major factor in adaptation. In animals, the frequency of alternative morphs, characterized by different morphologies and mating tactics, can be both condition-dependent and subject to rapid evolutionary change.     

Regulation of Bacterial Communities Through Antimicrobial Activity by the Coral Holobiont

Interactions between corals and associated bacteria and amongst these bacterial groups are likely to play a key role in coral health. However, the complexity of these interactions is poorly understood. We investigated the functional role of specific coral-associated bacteria in maintaining microbial communities on the coral Acropora millepora (Ehrenberg 1834) and the ability of coral mucus to support or inhibit bacterial growth. Culture-independent techniques were used to assess bacterial community structures whilst bacterial culture was employed to assess intra- and inter-specific antimicrobial activities of bacteria. Members of Pseudoalteromonas and ribotypes closely related to Vibrio coralliilyticus displayed potent antimicrobial activity against a range of other cultured isolates and grew readily on detached coral mucus. Although such bacterial ribotypes would be expected to have a competitive advantage, they were rare or absent on intact and healthy coral colonies growing in situ (analysed using denaturing gradient gel electrophoresis and 16S rRNA gene sequencing). The most abundant bacterial ribotypes found on healthy corals were Gammaproteobacteria, previously defined as type A coral associates. Our results indicate that this group of bacteria and specific members of the Alphaproteobacteria described here as ‘type B associates’ may be important functional groups for coral health. We suggest that bacterial communities on coral are kept in check by a combination of host-derived and microbial interactions and that the type A associates in particular may play a key role in maintaining stability of microbial communities on healthy coral colonies.     

Do bottlenecks increase additive genetic variance?

Because of anthropogenic factors many populations have been at least temporarily reduced to a very small population size. Such reductions could potentially decrease genetic variation and increase the probability of extinction. Analysis of molecular markers has shown a decrease in genetic variation but in many cases this has not reduced the ability of the population to recover from the bottleneck. This apparent paradox is resolved by a consideration of how population bottlenecks can affect additive genetic variance, the relevant measure of ability to respond to selective factors. A bottleneck has the potential to increase additive genetic variance in a population. This may result in an increase in fitness, particularly in populations of conservation concern that are small and lack genetic variation. Here we present a meta-analysis of experimental tests of this prediction using models designed to fit data that is strictly additive and data that has non-additive components. This analysis shows that additive genetic variance in a dataset dominated by morphological traits increases, on average, after a bottleneck event when the inbreeding coefficient is less than 0.3, but neither of the theoretical models alone can adequately explain this result. Because of our inability at present to predict the results of a population bottleneck in a specific case and the probability of extinction associated with small population size we caution against using bottlenecks to increase genetic variance, and thus the fitness, of endangered populations.     

Coral disease physiology: the impact of Acroporid white syndrome on <Emphasis Type="Italic">Symbiodinium</Emphasis>

Acroporid white syndrome, a disease-like syndrome from the Great Barrier Reef, results from degenerative host tissue at lesion borders. Tissue preceding lesion borders appears visually healthy, but it is currently unclear whether the endosymbiotic zooxanthellae (Symbiodinium) are physiologically impacted. Compared to healthy colonies, this study found no significant differences in symbiont density, mitotic index or chlorophyll a content in tissue bordering (0 cm), and 8 cm away from white syndrome lesions. Using chlorophyll a fluorescence techniques, the border tissue did not appear to be photosynthetically compromised, and Symbiodinium extracted from this area were photosynthetically competent. Transmission electron microscopy revealed extensive degeneration of host tissues surrounding symbionts in affected areas, however, Symbiodinium cells were structurally intact with no sign of in situ degradation. Collectively, these results suggest that Symbiodinium at white syndrome lesion borders exist in a dynamic intra-cellular state during active host tissue loss, yet remain physiologically uncompromised.     

Mass spawning aggregation of the giant bumphead parrotfish Bolbometopon muricatum

The present study reports a previously undocumented mass spawning aggregation and group spawning phenomena of c. 1200 individual bumphead parrotfish Bolbometopon muricatum in Palau, Micronesia. Although B. muricatum are protected in Palau, it is further recommended that management strategies should consider establishment of no‐take zones at B. muricatum spawning aggregations and concomitant sleeping grounds elsewhere.