Evol Ecol Res 19: 547-560 (2018) Full PDF if your library subscribes.
Individual phenotypic plasticity explains seasonal variation in sperm morphology in a passerine bird
Tim Schmoll1,2, Oddmund Kleven3 and Maria Rusche1
1Evolutionary Biology, Bielefeld University, Bielefeld, Germany, 2Institute of Evolutionary Ecology and Conservation Genomics, Ulm University, Ulm, Germany and 3Norwegian Institute for Nature Research (NINA), Trondheim, Norway
Correspondence: T. Schmoll, Evolutionary Biology, Bielefeld University, Konsequenz 45, 33615 Bielefeld, Germany. email: firstname.lastname@example.org
Background: Spermatozoa display marked variation in size and form among and within animal species. In birds, comparative evidence suggests that post-copulatory sexual selection resulting from extra-pair copulations is a major driver of interspecific variation in sperm traits. However, little is known about the extent, determinants, and dynamics of intraspecific variation in avian sperm traits.
Goal: Characterize and analyse variation in sperm morphology within and among two natural populations of great tits, Parus major, a socially monogamous passerine with frequent extra-pair matings.
Methods: We studied both a German and a Norwegian population of P. major. In the German population, we sampled spermatozoa during both the first clutch egg-laying and the nestling period (partly from the same individual males). In the Norwegian population, we sampled spermatozoa during the pre-laying/egg-laying period. We determined the overall size of spermatozoa as well as making separate measurements of sperm head, midpiece, and tail length.
Results: In the German population, spermatozoa were significantly shorter during the nestling period than during the egg-laying period. Individual phenotypic plasticity was responsible for the seasonal dynamics in sperm morphology. Changes in flagellum length (sum of midpiece and tail length) rather than changes in head length accounted for the change observed in total length. We found that changes in flagellum length were attributable to both midpiece and, in particular, tail shortening. Consequently, the ratio ‘midpiece/total length’ increased over the breeding cycle. Controlling statistically for seasonal variation, sperm total length was significantly repeatable across sperm samples from the same males. Furthermore, spermatozoa sampled in a Norwegian population early in the season differed from those obtained from the German population during egg-laying, but not from those obtained from the German population during the nestling period.
Conclusions: Individual phenotypic plasticity across the breeding season may contribute to intraspecific variation in avian sperm morphology. Our comparison across populations illustrates that seasonal variation in sperm dimensions within populations may confound between-population comparisons unless sampling date in relation to reproductive phenology is controlled for.
Keywords: great tit, individual phenotypic plasticity, Parus major, population divergence, repeatability, seasonality, sperm competition, sperm morphology.
DOWNLOAD A FREE, FULL PDF COPY
IF you are connected using the IP of a subscribing institution (library, laboratory, etc.)
or through its VPN.
© 2018 Tim Schmoll. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.
Subscribing institutions/libraries may grant individuals the privilege of making a single copy of an EER article for non-commercial educational or non-commercial research purposes. Subscribing institutions/libraries may also use articles for non-commercial educational purposes by making any number of copies for course packs or course reserve collections. Subscribing institutions/libraries may also loan single copies of articles to non-commercial libraries for educational purposes.
All copies of abstracts and articles must preserve their copyright notice without modification.