Utskrift
Tommi Nyman
Seniorforsker
-
Divisjon for miljø og naturressurser
(+47) 902 84 254 tommi.nyman@nibio.no Kontorsted: Svanhovd
The spatio-temporal evolution of woody plant lineages in the Holarctic is still understudied, limiting our understanding of evolutionary processes that promote higher diversity at higher latitudes in some lineages, which contradicts the latitudinal gradient hypothesis which predicts higher species richness in the tropics. Shrub willows (Salix subgenus Vetrix) comprise about 350 species of which many are adapted to arctic-alpine ecosystems and thus form an important element across the Holarctic region. In this study, we utilized RAD sequencing to estimate the spatio-temporal evolution of the Vetrix clade based on about 140 species covering most of its morphological and geographical diversity. The resolved phylogeny revealed four lineages: the Pan-Himalayan clade, the North American clade and two clades containing species from Eurasia. Widespread circumpolar species form a hybridogenetic grade between the Eurasian and North American clades. Our results confirm that shrub willows originated in the Tertiary, probably in Asia, and that diversification coincided with the climatic cooling in the Pleistocene. At least two radiations were observed, in the Pan Himalayas and in North America. Speciation was further shaped by migration and dispersal in Eurasia, likely accelerated by the uplift of mountain chains, the closure of the Turgai Strait and expansion of suitable habitats. The dated phylogeny revealed that speciation of arctic lineages predates adaptation to high latitudes, as also evident from the fossil record. Small wind-dispersed seeds enabled shrub willows to colonize the expanding arctic tundra regions in the Miocene and their recolonization after the LGM. Given the high observed number of polyploid species equally distributed in all clades and indications of genetic admixture, we assume that species diversity in shrub willows was additionally increased by hybridization and polyploidization.
While social network analysis was originally developed for human sociology studies, it is also a valuable tool for characterizing behavioural aspects in many animal populations. For instance, social network analysis can be used for assessing the transmission of diseases or information within groups. Here, we describe co-occurrences and potential social associations of ringed seals, Pusa hispida saimensis, in Lake Saimaa, Finland, from 2016 to 2022, based on photoidentification data. Throughout seven successive moulting seasons (April to June), we identified 425 individuals, of which 178 had pairwise co-occurrences in altogether 185 dyads. These seals had a variable number of associates (up to 10), and co-occurrences were observed in 1–7 years. In general, observations of pairs or larger groups of seals (up to five individuals) were rare, and mainly occurred in the two most densely populated basins of the lake. Most of the group observations occurred on ice rather than on rocks. Overall, the fragmented nature of the lake system, site fidelity and moulting habitat availability are key factors that probably affect the observed co-occurrences. Most of the dyads were observed during only one year, which may indicate social tolerance while using the same moulting site. However, 21 dyads were observed during multiple moulting seasons, with some at different sites separated by up to 3 km in different years, suggesting the existence of actual long-lasting associations. Our study represents the first description of co-occurrences and potential social associations in the endangered Saimaa ringed seal. These results can be used for designing and implementing mitigation strategies in case of unforeseen and sudden changes in the environment, such as a disease outbreak.
We studied the drivers of population-genetic structuring and genetic diversity in specialist parasites based on whole-genome resequencing data from 82 Echinophthirius horridus seal louse individuals sampled from 12 ecologically and behaviourally different phocine seal species, subspecies and populations across the Holarctic. We found that the main genetic disjunctions in E. horridus lice occur across seal host species and subspecies, with a further level of population subdivision emerging among host individuals within some populations. Endemic and relict landlocked seal (sub)species host the genetically most distinct louse populations, while lice associated with sympatric marine seals show signatures of occasional gene flow across hosts. Within the latter, the most extreme case is seen in the near-panmictic lice associated with northern European grey and harbour seals, which aggregate in shared rookeries and colonies. Although the louse and seal phylogenies were overall statistically significantly congruent, evidence for similar host shifts in the past is reflected in several conflicts in the phylogenetic trees of the lice and their hosts. Population-level mean heterozygosity and theta in seal lice varied considerably, and both measures of genetic variation were statistically significantly related to host population size. Taken together, our results support a non-adaptive model of parasite diversification, in which geographic and behavioural isolation among hosts drives parasite genetic differentiation, and genetic erosion in bottlenecked hosts cascades up to their specialist parasites. Our results provide new insights into processes that generate parasite diversity and trigger parallel losses of genetic diversity in endangered host–parasite systems.
Pollinatorene er truet. Dette får konsekvenser både for det biologiske mangfoldet og matsikkerheten vår. I WINGS skal vi utvikle løsninger for å etablere mer pollinatorvennlige kulturlandskap.
