Meeting Abstract

59.7  Wednesday, Jan. 6  First –day release and Dio2: a test of latitudinal variation in photoperiodic control of reproduction in great tits Parus major PERFITO, Nicole*; JEONG, Sunny; BENTLEY, George E.; SILVERIN, Bengt; HAU, Michaela; Max-Planck Institute for Ornithology, Germany and Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of Gothenburg, Sweden; Max-Planck Institute for Ornithology, Germany nperfito@berkeley.edu

In Europe, the species’ range of the great tit has expanded northward over the last 60 years. The threshold for photo-induction varies latitudinally among populations of great tits, with northern populations requiring longer days to induce gonadotropin secretion and testis growth than southern populations. We make use of these population differences in photoperiodic threshold to test the recently proposed model of photo-induction in quail. Namely, that gonadotropin-releasing hormone release is mediated by a local increase in triiodothronine (T3) as a result of up-regulation of type 2 iodothyronine deiodinase (DIO2) and down-regulation of type 3 iodothyronine deiodinase (DIO3) enzymes within cells in the basal hypothalamus. As southern populations are photostimulated by shorter day lengths, we predict that the increase in expression of key genes involved in the photo-induction pathway will occur earlier after lights on in southern than in northern population birds during one long day of photostimulation. We isolated total mRNA from brain tissue punches through the medial basal hypothalamus taken from alternate sides of 40-micron sections. We measured expression of several genes relative to a housekeeping gene using quantitative real-time PCR. These data will be the first to characterize changes in gene expression during photo-induction in any wild population. Furthermore, we aim to pin-point with these data at which point in this physiological cascade that natural selection has acted to alter timing of breeding.