From Micro to Macro: Investigating mechanisms involved in the convergent evolution of feather lice ecomorphs
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Authors
Grant, Avery
Issue Date
2023
Type
Dissertation
Language
Keywords
Evolution , Feather lice , Macroevolution , Molecular Convergence
Alternative Title
Abstract
Over the last hundreds of millions of years, the diversity of species that have evolved prompts questions about how and why species diversify and adapt to novel environments. In some instances, distantly related species will evolve similar traits, in a process called convergent evolution. These occurrences provide opportunities to investigate the mechanisms that drive species diversification and adaptation and whether different mechanisms can lead to similar evolutionary outcomes. Under what conditions is evolution repeatable? Are we able to predict how species may evolve under similar environments and selective pressures in the future? In some systems, distinct morphological traits emerge repeatedly among species that inhabit similar environments. Known as ecomorphs, these traits enable species to specialize within specific microhabitats. Such systems are ideal for studies investigating the mechanisms that drive the evolution of convergent traits. Here, we explore the evolution of ecomorphs in a host-parasite system from a micro and macroevolutionary perspective. Parasitic feather lice in the family Philopteridae (Order: Psocodea) are found on almost all species of birds and have repeatedly diversified into ecomorphs specific to areas of their host’s body. These morphological characteristics allow them to avoid being groomed off by the host. They have repeatedly evolved across their hosts since the Cretaceous-Paleogene boundary (~65 million years ago). Consequently, they have a long coevolutionary history with their hosts. Exploring the influence of different macroevolutionary events (e.g., cospeciation, duplication, and host-switching) across their evolutionary histories and the level of molecular convergence involved in ecomorph evolution can reveal some of the mechanisms involved in the convergence of feather lice ecomorphs. We began by assembling the protein coding genes of 57 species of feather lice to quantify the variation in GC content among and within species. Feather lice were GC poor (mean GC = 42.96%) with a significant amount of variation within and between species (GC range: 19.57-73.33%). Next, using the protein dataset we prepared in the previous study, we investigated molecular convergence of feather lice ecomorphs. For each ecomorph, candidate genes were selected if a minimum of two species of the same ecomorph were under positive selection. We found over 1,000 candidate genes for each ecomorph. Of these genes, a gene ontology (GO) analysis indicated that a smaller number of genes than expected were involved in gene expression (GO:0010467), which may suggest evolutionary constraints or strong stabilizing selection on regulatory processes. Additionally, wing ecomorphs had a disproportionate number of genes involved in biological and developmental processes. We found a significantly higher number of amino acid changes occurring at the same site than expected by chance for both body and head ecomorphs and fewer than expected for wing and generalists. Overall, we found evidence for molecular convergence at the gene level, particularly in wing ecomorphs. In this last project, we investigated these ecomorph transitions at a macroevolutionary scale. Specifically, we investigated how cospeciation, duplication, and host-switching events influenced ecomorph transitions. We found that macroevolutionary events play an important role in the convergent evolution of ecomorphs, with body and generalist ecomorphs significantly associated with duplication and host-switching events, respectively. We also found most transitions occur from a generalist state. These three studies have provided a better understanding of feather lice ecomorph evolution through a micro and macro lens. We show that feather lice, while GC poor, have a high level of variation in their base composition, which could reduce genetic constraints during convergent evolution. We identified molecular convergence at the gene level within feather lice ecomorphs. Further investigations into these genes and amino acid changes can provide more detailed results on the similarities and differences in molecular convergence. Specifically, future studies should measure the relative genotype and allele frequencies across feather lice to quantify standing genetic variation for which evolution can act upon. This would provide more information on the genetic constraints that influence molecular convergence. Cospeciation, duplication, and host-switching events also have a significant influence on ecomorph evolution. Identifying the different barriers feather lice ecomorphs experiencing during dispersal and establishment will improve our understanding of the macroevolutionary patterns across this group. Incorporating these new genetic findings into future macroevolutionary studies will enrich our understanding of the evolution and diversification of feather lice ecomorphs.