Biology subjects

Anderson, N. J.

Publications and source records attributed to Anderson, N. J..

3 recordsLinked to original sources

bioRxiv2024

Phenotypic divergence associated with genomic changes suggest local adaptation in obligate asexuals

Local adaptation is a key evolutionary process that generates global biodiversity and is promoted by environmental heterogeneity. Most of the existing knowledge on adaptive capacity is focused on sexual organisms, while the adaptation potential of asexually reproducing eukaryotes as well as their vulnerability to environmental change remains unclear. Cyclical parthenogens of the keystone freshwater grazer Daphnia are known to be locally adapted with genetic differentiation related to environmental conditions even between neighbouring ponds. Similar patterns have been found in obligate parthenogenetic congeners, however studies on their local adaptation potential are rare. Here, we use respiration rate and whole genome sequencing to test the local adaptation of Arctic asexual polyploid Daphnia from lakes with contrasting oxygen environments. The genomic data revealed the presence of two genetic clusters which differed significantly in respiration rates, suggesting molecular evolution as an adaptive mechanism. Functional enrichment pointed to differences in metabolic processes between the two genetic clusters. Our results, combining phenotypic and whole genome sequencing data, suggest that these clones are locally adapted to low oxygen concentrations and provide support for local adaptation by evolution in an obligate parthenogen.

evolutionary biology↗

bioRxiv2024

AMH regulates ovary size by counteracting ovarian follicle cluster effects.

Serum anti-Mullerian hormone (AMH) is the primary clinical indicator of mature oocyte counts in the ovaries, but its biological role remains poorly understood. Mammalian ovaries have a finite lifetime of oocytes that are slowly depleted as the dormant follicles housing the oocytes initiate maturation. Less than 0.1% of these follicles will reach maturity and ovulate an oocyte. Recent studies suggest that AMH is a key regulator that removes most of these follicles at early stages of follicle maturation. Most AMH is secreted as an inactive precursor protein, and we show that the required activating-enzymes are largely present outside the follicle. We then measured AMH concentrations in ovarian stroma with microdialysis showing that activity is confined to a short range from the site of secretion. To examine short-range interactions between follicles, we reconstructed the ovarian follicle positions from sheep ovaries in 3D space. This showed that most early follicles develop in proximity to more advanced follicles. Active immunisation of sheep against AMH to inhibit signalling, greatly expanded early follicle numbers, but almost entirely in proximity to large follicles. Large follicle proximity appears to greatly enhance early follicle survival, and AMH appears to attenuate this effect to prevent follicle overgrowth beyond sustainable limits.

physiology↗

bioRxiv2020

Centennial clonal stability of asexual Daphnia in Greenland lakes despite climate variability

Climate and environmental condition drive biodiversity at many levels of biological organisation, from populations to ecosystems. Combined with palaeoecological reconstructions, palaeogenetic information on resident populations provides novel insights into evolutionary trajectories and genetic diversity driven by environmental variability. While temporal observations of changing genetic structure are often made of sexual populations, little is known about how environmental change affects the long-term fate of asexual lineages. Here, we provide information on obligately asexual, triploid Daphnia populations from three Arctic lakes in West Greenland through the past 200-300 years to test the impact of a changing environment on the temporal and spatial population genetic structure. The contrasting ecological state of the lakes, specifically regarding salinity and habitat structure may explain the observed lake-specific clonal composition over time. Palaeolimnological reconstructions show considerable environmental fluctuations since 1700 (the end of the Little Ice Age), but the population genetic structure in two lakes was almost unchanged with at most two clones per time period. Their local populations were strongly dominated by a single clone that has persisted for 250-300 years. We discuss three possible explanations for the apparent population genetic stability: (1) the persistent clones are general purpose genotypes that thrive under broad environmental conditions, (2) clonal lineages evolved subtle genotypic differences that are unresolved by microsatellite markers, or (3) epigenetic modifications allow for clonal adaptation to changing environmental conditions. Our results will motivate research into the mechanisms of adaptation in these populations, as well as their evolutionary fate in the light of accelerating climate change in the polar regions.

ecology↗