Evolutionary Biology

Marxer, Monika; Barribeau, Seth; Schmid-Hempel, Paul

doi: 10.1007/s11692-015-9366-zpmid: N/A

Selection on basic growth properties of parasites may have many consequences for parasite traits, infection outcome, or host responses to infection. It is known that genotypes (strains) of the trypanosome parasite of bumblebees Crithidia bombi vary widely in their growth rates in their natural host, Bombus terrestris, as well as when cultured in medium. To test for changes in growth rates and their consequences, we here experimentally evolved six strains of C. bombi for fast and slow growth under controlled conditions in culture medium. Subsequently, we infected the evolved lines in live host and found that lines selected for slow growth attained higher infection intensity in the live bumblebee than those evolved for fast growth, whilst the immune response of the host was the same to both kinds of lines. These results fit the expectation that attenuation through rapid adaptation to a different environment, the culture medium, makes the parasite less successful in its next host. Selection for fast growth therefore does not necessarily lead to higher parasite success or more transmission. Hence, insect trypanosome pathogens can be attenuated by experimental evolution in the culture; this could inform important aspects of host-parasite evolution and perhaps vaccine development.

Parr, William; Wilson, Laura; Wroe, Stephen; Colman, Nicholas; Crowther, Mathew; Letnic, Mike

doi: 10.1007/s11692-016-9371-xpmid: N/A

Australia’s native wild dog, the dingo (Canis dingo), is threatened by hybridization with feral or domestic dogs. In this study we provide the first comprehensive three dimensional geometric morphometric evaluation of cranial shape for dingoes, dogs and their hybrids. We introduce a novel framework to assess whether modularity facilitates, or constrains, cranial shape change in hybridization. Our results show that hybrid and pure dingo morphology overlaps greatly, meaning that hybrids cannot be reliably distinguished from dingoes on the basis of cranial metrics. We find that dingo morphology is resistant, with observed hybrids exhibiting morphology closer to the dingo than to the parent group dog. We also find that that hybridization with dog breeds does not push the dingo cranial morphology towards the wolf phenotype. Disparity and integration analyses on the ten recovered modules provided empirical support for modularity facilitating shape change over short evolutionary time scales. However, our results show that this is may not be the case in hybridization events, which were not influenced by module integration or disparity levels. We conclude that although hybridization events may introduce breed dog DNA to the dingo population, the native cranial morphology, and therefore likely the feeding eco-niche, of the dingo population is resistant to change. Our results have implications for conservation and management of dingoes and, more broadly, for the influence of integration patterns over ecological time scales in relation to selection pressure.

Zelditch, Miriam; Calamari, Zachary; Swiderski, Donald

doi: 10.1007/s11692-016-9370-ypmid: N/A

Integrating studies of ontogeny with analyses of disparity can reveal important and surprising insights into the origins of disparity and why it varies among groups. One such potentially surprising insight is that disparity could be constant over ontogeny even though species differ in both rates and timings of development and in their ontogenetic changes in shape. Several studies of both primates and rodents have concluded that disparity is generated prenatally although some have concluded that it arises postnatally. However, neither constancy nor an ontogenetic increase in disparity has been ever been rigorously documented for either primates or rodents. For a small sample of rodents, we show that species differ in their postnatal ontogenies but infants are neither more nor less disparate than adults and the major dimensions of disparity distinguishing the main clades also do not change. The constancy in both the level of disparity and its main dimensions does not result primarily from the subtlety of postnatal differences. Those differences are indeed subtle but the disparity in directions of ontogenetic shape change is nonetheless sufficient to increase shape disparity significantly. Disparity does not increase postnatally primarily because ontogenies are not strictly linear; disparity generated postnatally counteracts that produced earlier. What limits the progressive accumulation of disparity is the curvature of ontogenetic trajectories, a curvature presumably due to ontogenetic changes in the spatial distribution of rates of bone deposition and resorption.

Guo, Cheng; Lu, Xin

doi: 10.1007/s11692-016-9367-6pmid: N/A

Body size of organisms as a fitness-related phenotype has evolved in response to local conditions, often through the size-dependent thermoregulatory mechanisms. The direction and degree of this response should depend on animals’ lifestyle in terms of the preference for terrestrial or aquatic conditions, especially so for adult anurans that differ in lifestyle among species but all must maintain certain body temperatures for metabolism. It may be expected that anuran species frequently exposed to terrestrial environments characterized by fluctuant thermal conditions are more plastic in body size along thermal gradients than those highly relaying on aquatic environments where thermal conditions are relatively stable. We test this prediction using both interspecific and intraspecific data. With anurans in China as the model organisms, we show that across terrestrial species but not aquatic species, body size decreases with increasing ambient temperature. From the published literature worldwide, we summarized that more terrestrial versus fewer aquatic species follow the predicted ecogeographical size patterns. In addition, both interspecific and intraspecific data reveal that arboreal anurans do not exhibit the size cline, probably because relatively warm climates experienced by these species impose weak selective pressures on heat conservation or adaptation to tree-climbing constrains the variation in body size. Our finding highlights the importance of taking lifestyle into account when assessing macroevolutionary trends in body size for anurans in particular and ectothermic taxa in general.

Kahar, Siim; Debes, Paul; Vuori, Kristina; Vähä, Juha-Pekka; Vasemägi, Anti

doi: 10.1007/s11692-016-9368-5pmid: N/A

Oxidative stress (OS) may pose important physiological constraints on individuals, affecting trade-offs between growth and reproduction or ageing and survival. Despite such evolutionary and ecological importance, the results from studies on the magnitude of individual variation in OS resistance and the underlying causes of this variation such as genetic, environmental, and maternal origins, remain inconclusive. Using a high throughput methodology, we investigated the activity levels in three OS resistance-related enzymes (superoxide dismutase, SOD; glutathione reductase, GR; glutathione S-transferase, GST) during the early life stages of 1000 individuals from 50 paternal half-sib families in two populations of Atlantic salmon. Using animal mixed models, we detected the presence of narrow-sense heritability for SOD and GST; that for GST differed between populations due to differences in environmental variance. We found support for the presence of common environmental variation, including maternal effects, for only GR. Using a bivariate animal model, we detected a positive environmental correlation between activity levels of SOD and GST but were unable to detect an additive genetic correlation. Our results complement previous heritability findings for levels of reactive oxygen species or OS resistance by demonstrating the presence of heritability for OS-related enzyme activities. Our findings provide a foundation for future work, such as investigations on the evolutionary importance of variation in enzyme activities. In addition, our findings emphasise the importance of accounting for developmental stage, environmental variance, and kin relationships when investigating the OS-response at the enzyme activity level.

Fitzhugh, Kirk

doi: 10.1007/s11692-016-9381-8pmid: N/A

Crother and Murray (Cladistics 31: 573–574, 2015) criticize the statement by Assis (Cladistics 30: 240–242, 2014) that phylogenetic hypotheses are amenable to testing but not falsification. The claims by both sets of authors are based on long-standing misconceptions about testing developed within systematics. Testing phylogenetic hypotheses confuses the inferences of those hypotheses by way of abductive reasoning with their being tested via induction. Cladograms lack the causal details of the different hypotheses implied by those diagrams to make testing feasible, and falsification has been shown to be problematic for historical sciences.