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Sperm Evolution in Birds

Why are sperm cells so variable among species?

images of birds and microscope images of their respective sperm cells

The sperm heads of Reed Bunting, Willow Warbler and European Nuthatch (top to bottom) illustrate the typical helical passerine sperm and its variation in size and shape among species. Arrows indicate the transitions between the acrosome and the nucleus, and the nucleus and the flagellum. 

Introduction

Biological sex is defined by the size of the gametes. Males produce tiny gametes in huge numbers (sperm), females produce large and few (eggs). Still, there is a remarkable variation in the size and shape of gametes, in particular of sperm. This is especially true for the most species-rich order of birds, the Passeriformes or "perching birds".

Background

An unanswered question in evolutionary biology is why sperm cells have become so diversified across the animal kingdom. Over the last 10-15 years our research group has made significant contributions to the study of sperm form and function in passerine birds. This project seeks to increase our knowledge of the mechanisms of how sperm cells evolve and diversify in these species. We will reconstruct the evolutionary history of sperm diversification across the 140 families of passerine birds and identify major innovations/shifts in sperm morphology. We will explore the genetic architecture of various sperm components, how these genes are regulated during spermatogenesis, and how the major shifts in sperm evolution can be explained at the genetic and genomic level. We will also explore the types of Darwinian selection acting on sperm phenotypes. We combine our own expertise on sperm phenotypes with external expertise on functional and comparative genomics, and with ongoing, long-term population studies of selected species where the fitness of sperm phenotypes (i.e. fertilization success) can be measured in a competitive context. The project has the potential to advance our understanding of some fundamental questions in biology, such as the "evolution of sperm diversification" and "the genetics of a phenotype", which have relevance to all species with sexual reproduction.

Publications

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  • Yilma, Zelealem Belaineh & Lifjeld, Jan Terje (2022). Selection on sperm size in response to promiscuity and variation in female sperm storage organs.
  • Cramer, Becky; Yilma, Zelealem Belaineh & Lifjeld, Jan Terje (2022). Selection on sperm size in response to promiscuity and variation in female sperm storage organs.
  • Cramer, Becky; Whittington, Emma & Garlovsky, Martin (2022). Diversity and evolution in sperm, ova, and other primary reproductive traits.
  • Cramer, Emily Rebecca Alison (2021). Sperm as a reproductive barrier between passerine species.
  • Lifjeld, Jan Terje (2021). A museum collection of bird sperm.
  • Cramer, Becky; Grønstøl, Gaute; Maxwell, Logan; Kovach, Adrienne & Lifjeld, Jan Terje (2021). Sperm divergence as a potential reproductive barrier in Ammospiza sparrows (and other passerines).

View all works in Cristin

Published Aug. 13, 2022 10:52 AM - Last modified Sep. 2, 2022 4:02 PM