Projects / Programmes
Evolutionary dead ends: The perils of extreme phenotypes
| Code |
Science |
Field |
Subfield |
| 1.03.00 |
Natural sciences and mathematics |
Biology |
|
| Code |
Science |
Field |
| B005 |
Biomedical sciences |
Zoology |
| Code |
Science |
Field |
| 1.06 |
Natural Sciences |
Biological sciences |
Evolution, diversification, extinction, biodiversity, spiders
Researchers (15)
Organisations (2)
Abstract
Evolutionary dead ends predict cessation of evolutionary progression and diversification, or even lineage extinction, due to a specific organismal trait. Such a trait may initially secure fitness advantages, but in the long run these advantages are lost, and the trait becomes costly. Organismal traits that have been suggested to cause evolutionary dead ends relate to life histories, mating systems, ecological specializations, or interspecific interactions, but literature rarely establishes direct links between traits and lineage extinction. The aim of our research agenda is to evaluate whether extreme phenotypes could represent dead end traits. By “extreme” we refer to exaggerated sizes, sexually conflicted behaviors, or ecological adaptation to extreme environments.
Spiders represent an ideal study group in this respect. Certain spiders exhibit the most extreme sexual size dimorphism (SSD; large females, small males) among terrestrial animals, with correspondingly giant web sizes, and with seemingly co-occurring sexually conflicted mating rituals. These extremely dimorphic spider clades are geographically and ecologically widespread but are relatively species poor. A combination of their morphology, web architecture, and mating biology on the one hand, and their evolutionary history and low diversity on the other, may imply a correlation between extreme phenotypes and long-term evolutionary decline. However, this link has never been unequivocally established.
We will explore potential links between extreme invertebrate phenotypes, exemplified by sexual size dimorphism, exaggerated web size, and sexually conflicted behaviors in selected groups and species of spiders, and the evolutionary patterns of those lineages. Using a combination of micro- and macroevolutionary analyses we will test whether extreme phenotypes represent evolutionary dead ends. We hypothesize that the evolution of extreme phenotypes triggers benefits only in the short (ecological) time, but incurs long-term (evolutionary) costs.
Our first work package will quantify extremeness in phenotypic traits, and will test whether exaggerated web sizes and sexually conflicted behaviors co-vary with SSD. A positive phylogenetic correlation of these phenotypes would imply their concerted evolution. The second work package will experimentally test predictions from the differential equilibrium model of SSD evolution. This model features context-specific drivers of gender size variation that result in clade-specific SSD. We predict that giant females will exhibit fecundity advantages over smaller females, and these will outweigh the physiological costs of gigantism in the foraging context (silk production for web construction). On the other hand, pre- and post-copulatory sexual selection processes will favor intermediate sized males. The potential validity of the model will reinforce the view that SSD evolves in response to gender specific additive selection effects, and that SSD is more extreme in those species that exhibit weaker cross-sex genetic correlation.
The third work package will identify long-term manifestations of extreme phenotypes in order to test the prediction that extreme phenotypes can decelerate diversification and accelerate extinction. We will employ phylogenetic and comparative tests to establish how species richness in comparable clades varies with phenotypic "extremeness". We will model global extinction propensity of extreme phenotypes in the tropics versus temperate zones, then evaluate the validity of these models with real observations of global diversity in targeted clades. In comparison with a sister lineage or a lineage with a comparable evolutionary history, a disproportionately species depauperate lineage with extreme phenotypes would implicate that suite of phenotypes to be associated with long-term macroevolutionary risks, limiting diversification and promoting extinction.
Significance for science
The relevance of the project as envisioned from the expected results lies in our ability to generalize how trait evolution can potentially provide benefits in the ecological time from generation to generation, but also incur costs and pitfalls in the evolutionary time. Our evolutionary research agenda is novel in combining phylogenetic, comparative morphological, behavioral, physiological, ecological, molecular, and quantitative genetic approaches to generalize about selection for and against extreme phenotypes, and to scrutinize their long term evolutionary consequences. A combination of these approaches has never been applied in the context of extreme phenotypic evolution in spiders. Studies on evolutionary dead ends in spiders have so far been limited to the handful of social clades, focusing solely on the rare phenomenon of sociality. Our proposed study is therefore pioneering in identifying the key traits responsible for evolutionary cessation, and possibly extinction, also in the solitary groups to which the vast majority of the over 46 thousand spider species belong. Furthermore, the potential for traits to represent dead ends is poorly explored in any animal group, and thus our project may provide important new insights into trait adaptiveness in general. We expect that our products, from top-tier scientific papers to public outreach, will be broadly interesting and relevant for evolutionary biology on the one hand, and popularity of science on the other. This project also has a strong training component, with an age- and gender balanced blend of senior researchers, early career scientists, and graduate students.
Significance for the country
The relevance of the project as envisioned from the expected results lies in our ability to generalize how trait evolution can potentially provide benefits in the ecological time from generation to generation, but also incur costs and pitfalls in the evolutionary time. Our evolutionary research agenda is novel in combining phylogenetic, comparative morphological, behavioral, physiological, ecological, molecular, and quantitative genetic approaches to generalize about selection for and against extreme phenotypes, and to scrutinize their long term evolutionary consequences. A combination of these approaches has never been applied in the context of extreme phenotypic evolution in spiders. Studies on evolutionary dead ends in spiders have so far been limited to the handful of social clades, focusing solely on the rare phenomenon of sociality. Our proposed study is therefore pioneering in identifying the key traits responsible for evolutionary cessation, and possibly extinction, also in the solitary groups to which the vast majority of the over 46 thousand spider species belong. Furthermore, the potential for traits to represent dead ends is poorly explored in any animal group, and thus our project may provide important new insights into trait adaptiveness in general. We expect that our products, from top-tier scientific papers to public outreach, will be broadly interesting and relevant for evolutionary biology on the one hand, and popularity of science on the other. This project also has a strong training component, with an age- and gender balanced blend of senior researchers, early career scientists, and graduate students.
Most important scientific results
Interim report
Most important socioeconomically and culturally relevant results
Interim report
