Discovering climatic, life history, and biogeographic effects on animal and plant Population Genetic Diversity: assessing the myths
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Genetic variation is advantageous for organisms because it allows adaptations to the environment via natural selection and altering allele frequency, therefore increasing the likelihood of thriving in one’s current environment. Genetic diversity is impacted by genetic drift and human-mediated environmental changes, the latter of which disrupt population and community dynamics that lead to species extinction and loss of ecosystem services, and thus have a drastic impact on how ecosystems function (De Kort et al. 2021).
Previous studies have investigated how population genetic diversity (GDP) varies among life-history traits (longevity, body size, fecundity) and biogeography (the position of each population relative to the core and edges of the species’ range) independently, but none have studied the interdisciplinary effects that these have on genetic diversity. As such, researchers set out to investigate the relationship and interactions between climatic, biogeographic, historical, and life-history-related factors. Population genetic diversity is measured as multilocus expected heterozygosity. Scientists have identified these factors that contribute to a change in GDP, but we are left with a question: how do these factors intertwine or overlap to impact GDP? And, how accurate are previously established theories regarding the effects of biogeography on population genetic diversity?
Conservation programs often use “evolutionary significant units” which depend of GDP. Consequently, conservation efforts remain a significant priority within the ecology field in order to preserve the globe’s biodiversity.
De Kort et al. synthesized published datasets to inform GDP patterns across a global and taxonomic scale, with the goal of determining the main life-history related, past and current climatic, and biogeographic factors that sustain GDP patterns. Taxonomic data came from 8356 populations distributed around the world and of different taxa, from pines and monocots, to mammals and reptiles.
The data is disputed. Some studies have made significant findings regarding high genetic diversity within wind-pollinated plant populations as well as small animals with high fecundity and short longevity, whereas others have claimed that they could not affirm those results and conclusions (De Kort et al. 2021). Likewise, we are faced with conflicting data results regarding theories that are thought to have an influence on population genetic diversity. One such example is the core-periphery hypothesis, which predicts that populations positioned at the edge of a species’ range (or, lifetime location/s) should have lower genetic variation due to low connectivity and founder effects; on the other hand, their counterparts located at the center of the species range usually possess higher levels of GDP because of an increased admixture of lineages (Duncan et al. 2015; Matute 2013).
The Equator hypothesis is another theory that researchers sought out to evaluate. This hypothesis states that population genetic diversity is highest across the Equator due to a maintenance of climate conditions and decreases with distance. Another postulation is that higher temperatures increase mutation rates and therefore increase GDP.
Results of the study provided key insights into the differences between plant and animal GDP, namely that animals have a higher general GDP than plants. Reasons for why animals experience a higher level of GDP include that the vertebrates selected mate through outcrossing and active movement, whereas plants rely on passive movement through pollen and seed dispersal which likely reduces plant GDP.
The study found that for animals precipitation, temperature, elevation, and the combined body size/longevity factor had a significant impact on GDP across all phyla, with a higher observed GDP for populations living in habitats with high precipitation and temperature, low elevation, and small and short-lived species.
In plants, however, we see differences, namely that highest GDP is found in longer-lived species. Meanwhile for plants we observe that precipitation had a negative impact on GDP. Interestingly, precipitation has been noted as a dominant driver of natural selection in over 150 plant and animal species. This opposing result prompts us to question the role that precipitation plays as an evolutionary force for both kingdoms.
Findings did provide evidence supporting the core-periphery hypothesis, with animal GDP highest in core populations and gradually decreased toward the periphery populations.
Results did not align with the Equator hypothesis: in animals, only the mollusk and amphibian species demonstrated this pattern, and in plants we observed a slight increase in GDP with increasing distance from the equator in eucidot plants.
Questions remain about the efficacy of the current GDP study method, as there is a large discrepancy in population genetic diversity among current study data. As such, we need to find a more universal mold.
Next steps for conservation include looking at GDP on the species-specific scale to gain a better sense of appropriate models, knowing the geographic position of sampled populations, and looking at new factors for further analysis. Examples of some factors include animal gamete dispersal and strategies of space use (migratory, nomadic, and dispersal behavior), allelic richness, adaptive genetic variation, and epigenetic variation. Looking at these variables would aid us in keeping up with the effects of anthropogenic stressors, long-term adaptive potential, and changes in environment. We also need to consider that long-living plant species pose an additional risk as they respond slower to reduced gene flow, which is commonly caused by habitat fragmentation.
What species will be chosen first? How do we select which species should be prioritized, when so many face the threat of extinction in our current climate? How can we use single nucleotide polymorphisms to investigate the relationship between population genetic diversity and extinction risk?
Svenja Nanfelt is a senior biology major at Davidson College. Contact her at svnanfelt@davidson.edu.
References
De Kort, H., Prunier, J.G., Ducatez, S. et al. Life history, climate and biogeography interactively affect worldwide genetic diversity of plant and animal populations. Nat Commun 12, 516 (2021).
Duncan SI, Crespi EJ, Mattheus NM, Rissler LJ. History matters more when explaining genetic diversity within the context of the core-periphery hypothesis. Mol Ecol. 2015 Aug;24(16):4323-36. doi: 10.1111/mec.13315. Epub 2015 Aug 6. PMID: 26175277.
Matute DR. The role of founder effects on the evolution of reproductive isolation. J Evol Biol. 2013 Nov;26(11):2299-311. doi: 10.1111/jeb.12246. Epub 2013 Oct 1. PMID: 24118666.
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