Ellen Nikelski

Bio: Ellen Nikelski is an academic researcher from University of Toronto. The author has contributed to research in topics: Nuclear gene & Mitochondrial DNA. The author has co-authored 1 publications.

Mitonuclear co-introgression opposes genetic differentiation between phenotypically divergent songbirds

Abstract: Comparisons of genomic variation among closely related species often show more differentiation in mitochondrial DNA (mtDNA) and sex chromosomes than in autosomes, a pattern expected due to the relative effective population sizes of these genomic components. Differential introgression can cause some species pairs to deviate dramatically from this pattern. The yellowhammer (Emberiza citrinella) and the pine bunting (E. leucocephalos) are hybridizing avian sister species that differ greatly in appearance but show no mtDNA differentiation. This discordance might be explained by mtDNA introgression--a process that can select for co-introgression at nuclear genes with mitochondrial functions (mitonuclear genes). We investigated genome-wide nuclear differentiation between yellowhammers and pine buntings and compared it to what was seen previously in the mitochondrial genome. We found clear nuclear differentiation that was highly heterogeneous across the genome, with a particularly wide differentiation peak on the sex chromosome Z. We further tested for preferential introgression of mitonuclear genes and detected evidence for such biased introgression in yellowhammers. Mitonuclear co-introgression can remove post-zygotic incompatibilities between species and may contribute to the continued hybridization between yellowhammers and pine buntings despite their clear morphological and genetic differences. As such, our results highlight the potential ramifications of co-introgression in species evolution.

Responses of Yellowhammer Emberiza citrinella, Pine Bunting E. leucocephalos and Their Hybrids to Playbacks of Con- and Heterospecific Songs and Calls in a Hybrid Zone

Abstract: Yellowhammers Emberiza citrinella and Pine Buntings E. leucocephalos hybridize in a c. 2500 km wide sympatric zone in northwest Asia. In the centre of this zone, over the last 50 years males with Yellowhammer and intermediate (i.e. hybrid) phenotypes have been replacing the Pine Bunting phenotype. In the southern part of the zone by contrast, the Pine Bunting phenotype is still common. In this study, we asked if there is a behavioural asymmetry between males depending on their phenotypes and whether this asymmetry can explain phenotypic compositions observed in different parts of the hybrid zone. This study was performed in 2017–2019 in Altai Republic, Russia, in the southern part of the hybrid zone. Songs of Yellowhammer and Pine Bunting are generally similar, although they differ in details. The species also differ in usage of call repertoires: the ‘see’ call is more characteristic for Yellowhammer, while the ‘zieh’ call is used more frequently by Pine Bunting. We performed playback experiments using contrasting stimuli to evaluate responses towards (1) Pine Bunting song vs. Yellowhammer song and (2) songs coupled with ‘zieh’ calls vs. songs coupled with ‘see’ calls. Experiments showed that Yellowhammer and hybrid males were more aggressive towards other males than were birds with the Pine Bunting phenotype. Therefore, the latter might be at a disadvantage in territory acquisition and maintenance. At the same time, males of any phenotype responded more strongly to Yellowhammer playback than to Pine Bunting playback, and to the ‘see’ call than to the ‘zieh’ call. This might counterbalance the competitive ability of different phenotypes in territorial competition, thus allowing Pine Bunting males to avoid being displaced by more aggressive Yellowhammer and hybrid males in the southern part of the hybrid zone.

Биологический вид — реальность или абстракция? Занимательная история про двух овсянок, "Природа"

Abstract: Главный вопрос в проблеме вида: существуют ли виды на самом деле или это лишь абстрактная таксономическая категория, придуманная систематиками для описания биологического разнообразия Решить дилемму «либо виды без эволюции, либо эволюция без видов» можно, логически обосновав, что переходных форм между подвидом и видом должно быть мало. В рамках биологической концепции вида таким обоснованием служит гипотеза усиления: в гибридной зоне естественный отбор направлен на совершенствование механизмов этологической изоляции, т.е. при установлении вторичного контакта процесс видообразования ускоряется. Ключевым моментом этой гипотезы является утверждение о пониженной приспособленности гибридов, возникающей вследствие разрушения у них коадаптированных генных комплексов родительских форм, механизм формирования которых описывает модель Добржанского—Мёллера. С целью оценки эффективности механизмов репродуктивной изоляции и жизнеспособности гибридов проведен многолетний мониторинг гибридной популяции обыкновенной и белошапочной овсянок на Алтае. Оказалось, что гибриды действительно меньше живут, чем птицы с фенотипами родительских видов, что подтверждает гипотезу Добржанского—Мёллера, хотя гипотеза усиления в данном случае своего подтверждения не находит.