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Evolutionarily Labile (evolutionarily + labile)
Selected AbstractsEvolution of latex and its constituent defensive chemistry in milkweeds (Asclepias): a phylogenetic test of plant defense escalationENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 1 2008Anurag A. Agrawal Abstract A tremendous diversity of plants exude sticky and toxic latex upon tissue damage, and its production has been widely studied as a defensive adaptation against insect herbivores. Here, we address variation in latex production and its constituent chemical properties (cardenolides and cysteine proteases) in 53 milkweeds [Asclepias spp. (Apocynaceae)], employing a phylogenetic approach to test macroevolutionary hypotheses of defense evolution. Species were highly variable for all three traits, and they showed little evidence for strong phylogenetic conservatism. Latex production and the constituent chemical defenses are thus evolutionarily labile and may evolve rapidly. Nonetheless, in phylogenetically independent analyses, we show that the three traits show some correlations (and thus share a correlated evolutionary history), including a positive correlation between latex exudation and cysteine protease activity. Conversely, latex exudation and cysteine protease activity both showed a trade-off with cardenolide concentrations in latex. We also tested whether these traits have increased in their phenotypic values as the milkweeds diversified, as predicted by plant defense escalation theory. Alternative methods of testing this prediction gave conflicting results , there was an overall negative correlation between amount of evolutionary change and amount of latex exudation; however, ancestral state reconstructions indicated that most speciation events were associated with increases in latex. We conclude by (i) summarizing the evidence of milkweed latex itself as a multivariate defense including the amount exuded and toxin concentrations within, (ii) assessing the coordinated evolution of latex traits and how this fits with our previous notion of ,plant defense syndromes', and finally, (iii) proposing a novel hypothesis that includes an ,evolving community of herbivores' that may promote the escalation or decline of particular defensive strategies as plant lineages diversify. [source] Evolution of cranial development and the role of neural crest: insights from amphibiansJOURNAL OF ANATOMY, Issue 5 2005James Hanken Abstract Contemporary studies of vertebrate cranial development document the essential role played by the embryonic neural crest as both a source of adult tissues and a locus of cranial form and patterning. Yet corresponding and basic features of cranial evolution, such as the extent of conservation vs. variation among species in the contribution of the neural crest to specific structures, remain to be adequately resolved. Investigation of these features requires comparable data from species that are both phylogenetically appropriate and taxonomically diverse. One key group are amphibians, which are uniquely able to inform our understanding of the ancestral patterns of ontogeny in fishes and tetrapods as well as the evolution of presumably derived patterns reported for amniotes. Recent data support the hypothesis that a prominent contribution of the neural crest to cranial skeletal and muscular connective tissues is a fundamental property that evolved early in vertebrate history and is retained in living forms. The contribution of the neural crest to skull bones appears to be more evolutionarily labile than that of cartilages, although significance of the limited comparative data is difficult to establish at present. Results underline the importance of accurate and reliable homology assessments for evaluating the contrasting patterns of derivation reported for the three principal tetrapod models: mouse, chicken and frog. [source] Empirical tests of life-history evolution theory using phylogenetic analysis of plant demographyJOURNAL OF ECOLOGY, Issue 2 2010Jean H. Burns Summary 1. A primary goal of evolutionary ecology is to understand factors selecting for the diversity of life histories. Life-history components, such as time-to-reproduction, adult survivorship and fecundity, might differ among species because of variation in direct and indirect benefits of these life histories in different environments or might have lower-than-expected variability because of phylogenetic constraints. Here, we present a phylogenetic examination of demography and life histories using a data base of 204 terrestrial plant species. 2. Overall, statistical models without phylogeny were preferred to models with phylogeny for vital rates and elasticities, suggesting that they lacked phylogenetic signal and are evolutionarily labile. However, the effect of phylogeny was significant in models including sensitivities, suggesting that sensitivities exhibit greater phylogenetic signal than vital rates or elasticities. 3. Species with a greater age at first reproduction had lower fecundity, consistent with a cost of delayed reproduction, but only in some habitats (e.g. grassland). We found no evidence for an indirect benefit of delayed reproduction via a decrease in variation in fecundity with age to first reproduction. 4. The greater sensitivity and lower variation in survival than in fecundity was consistent with buffering of more important vital rates, as others have also found. This suggests that studies of life-history evolution should include survival, rather than only fecundity, for the majority of species. 5.Synthesis. Demographic matrix models can provide informative tests of life-history theory because of their shared construction and outputs and their widespread use among plant ecologists. Our comparative analysis suggested that there is a cost of delayed reproduction and that more important vital rates exhibit lower variability. The absolute importance of vital rates to population growth rates (sensitivities) exhibited phylogenetic signal, suggesting that a thorough understanding of life-history evolution might require an understanding of the importance of vital rates, not just their means, and the role of phylogenetic history. [source] Genetic basis of differential opsin gene expression in cichlid fishesJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2010K. L. CARLETON Abstract Visual sensitivity can be tuned by differential expression of opsin genes. Among African cichlid fishes, seven cone opsin genes are expressed in different combinations to produce diverse visual sensitivities. To determine the genetic architecture controlling these adaptive differences, we analysed genetic crosses between species expressing different complements of opsin genes. Quantitative genetic analyses suggest that expression is controlled by only a few loci with correlations among some genes. Genetic mapping identifies clear evidence of trans-acting factors in two chromosomal regions that contribute to differences in opsin expression as well as one cis-regulatory region. Therefore, both cis and trans regulation are important. The simple genetic architecture suggested by these results may explain why opsin gene expression is evolutionarily labile, and why similar patterns of expression have evolved repeatedly in different lineages. [source] | ||||||||||