Browsing by Subject "PROTANDRY"

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  • Velmala, William; Helle, Samuli; Ahola, Markus P.; Klaassen, Marcel; Lehikoinen, Esa; Rainio, Kalle; Sirkiä, Päivi; Laaksonen, Toni (2015)
    For migratory birds, the earlier arrival of males to breeding grounds is often expected to have fitness benefits. However, the selection differential on male arrival time has rarely been decomposed into the direct effect of male arrival and potential indirect effects through female traits. We measured the directional selection differential on male arrival time in the pied flycatcher (Ficedula hypoleuca) using data from 6years and annual number of fledglings as the fitness proxy. Using structural equation modeling, we were able to take into account the temporal structure of the breeding cycle and the hierarchy between the examined traits. We found directional selection differentials for earlier male arrival date and earlier female laying date, as well as strong selection differential for larger clutch size. These selection differentials were due to direct selection only as indirect selection for these traits was nonsignificant. When decomposing the direct selection for earlier male arrival into direct and indirect effects, we discovered that it was almost exclusively due to the direct effect of male arrival date on fitness and not due to its indirect effects via female traits. In other words, we showed for the first time that there is a direct effect of male arrival date on fitness while accounting for those effects that are mediated by effects of the social partner. Our study thus indicates that natural selection directly favored earlier male arrival in this flycatcher population.
  • Lehikoinen, Aleksi; Santaharju, Jarkko; Pape Moller, Anders (2017)
    Multiple studies have investigated differential migration of sexes during spring migration, while such differences during autumn migration are poorly studied. We tested several functional hypotheses explaining differences in autumnmigration dates between sex and age classes and whether these patterns vary between short- and long-distance migrants (SDMs and LDMs, respectively). We used data of ringed birds from the Hanko and Lagsar Bird Observatory, Finland, North Europe. Altogether data for c. 200,000 ringed birds including 14 passerine species were used. Protogyny, with females migrating earlier than males, was common among young birds, and this difference was clearer in LDMs than in SDMs. However, in adults protogyny was not found, whereas protandy, with females migrating earlier than females, was found in two species. Furthermore, species-specific sexual size dimorphism, SSD, was significantly connected with the time differences in migration between the sexes in SDMs, but not in LDMs. These results suggest that multiple factors are likely affecting differential timing of autumnmigration in birds. It can be beneficial for males, especially young birds, to spend additional time at the breeding grounds to prospect for future nesting sites. The connection between SSD and autumn migration dates in SDM could be linked with the pattern where larger sized individuals can winter closer to the breeding grounds. In addition, later migration dates of adult females compared to adult males could suggest that larger reproductive investment by adult females on breeding may delay their autumn migration.