So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Climate change 2014 - Synthesis Report

A consequence of climate change is the increased frequency and severity of extreme heat waves. This is occurring now as most of the warmest summers and most intense heat waves ever recorded have been during the past decade. In this review, I describe the ways in which animals and human populations are likely to respond to increased extreme heat, suggest how to study those responses, and reflect on the importance of those studies for countering the devastating impacts of climate change.

Heat Waves, the New Normal: Summertime Temperature Extremes Will Impact Animals, Ecosystems, and Human Communities

Summary 1. Our study addresses the role of non-genetic and genetic inheritance in shaping the adaptive potential of populations under a warming ocean scenario. We used a combined experimental approach [transgenerational plasticity (TGP) and quantitative genetics] to partition the relative contribution of maternal vs. paternal (additive genetic) effects to offspring body size (a key component of fitness), and investigated a potential physiological mechanism (mitochondrial respiration capacities) underlying whole-organism growth/size responses. 2. In very early stages of growth (up to 30 days), offspring body size of marine sticklebacks benefited from maternal TGP: offspring of mothers acclimated to 17 °C were larger when reared at 17 °C, and offspring of mothers acclimated to 21 °C were larger when reared at 21 °C. The benefits of maternal TGP on body size were stronger and persisted longer (up to 60 days) for offspring reared in the warmer (21 °C) environment, suggesting that maternal effects will be highly relevant for climate change scenarios in this system. 3. Mitochondrial respiration capacities measured on mature offspring (F1 adults) matched the pattern of TGP for juvenile body size, providing an intuitive mechanistic basis for the maternal acclimation persisting into adulthood. Size differences between temperatures seen at early growth stages remained in the F1 adults, linking offspring body size to maternal inheritance of mitochondria. 4. Lower maternal variance components in the warmer environment were mostly driven by mothers acclimated to ambient (colder) conditions, further supporting our tenet that maternal effects were stronger at elevated temperature. Importantly, all parent–offspring temperature combination groups showed genotype 9 environment (G 9 E) interactions, suggesting that reaction norms have the potential to evolve. 5. To summarize, TGP and G 9 E interactions work in concert to mediate impacts of ocean warming on metabolic capacity and early growth of marine sticklebacks. TGP can buffer short-term detrimental effects of climate warming and may buy time for genetic adaptation to catch up, therefore markedly contributing to the evolutionary potential and persistence of populations under climate change.

Transgenerational plasticity in marine sticklebacks: maternal effects mediate impacts of a warming ocean

Since late 2014, the Mexican Caribbean coast has periodically received massive, atypical influxes of pelagic Sargassum spp. (sargasso). Negative impacts associated with these influxes include mortality of nearshore benthic flora and fauna, beach erosion, pollution, decreasing tourism and high management costs. To understand the dynamics of the sargasso influx, we used Landsat 8 imagery (from 2016 to mid-2020) to record the coverage of sargasso in the sea off the Mexican Caribbean coastline, with a maximum reported in September 2018. Satellite image analysis also showed local differences in the quantity of beached sargasso along the coastline. Over the years, good practice for collection on the beach and for off-shore collection of sargasso have been established through trial and error, and the Mexican Government and hotel industry have spent millions of dollars on removal and off-shore detention of sargasso. Notwithstanding, sargasso also has various properties that could be harnessed in local industries. The stimulation of local industrial growth would offer alternatives to the dependence on tourism, as a circular economy, based on sargasso, is developed.

Massive Influx of Pelagic Sargassum spp. on the Coasts of the Mexican Caribbean 2014–2020: Challenges and Opportunities

Molluscs are the second most species-rich phylum in the animal kingdom, yet only eleven genomes of
this group have been published so far. Here, we present the draft genome sequence of the pulmonate
freshwater snail Radix auricularia . Six whole genome shotgun libraries with different layouts were
sequenced. The resulting assembly comprises 4,823 scaffolds with a cumulative length of 910 Mb and
an overall read coverage of 72x. The assembly contains 94.6 % of a metazoan core gene collection,
indicating an almost complete coverage of the coding fraction. The discrepancy of ~690 Mb compared
to the estimated genome size of R. auricularia (1.6 Gb) results from a high repeat content of 70 %
mainly comprising DNA transposons. The annotation of 17,338 protein coding genes was supported
by the use of publicly-available transcriptome data. This draft will serve as starting point for further
genomic and population genetic research in this scientifically important phylum.

/pdf/an-annotated-draft-genome-for-radix-auricularia-gastropoda-1rh6g2kvba.pdf

An annotated draft genome for Radix auricularia (Gastropoda, Mollusca).

With both global surface temperatures and the incidence and intensity of extreme temperature events projected to increase, the assessment of species' sensitivity to chronic and acute changes in temperature has become crucial. Sensitivity predictions are based predominantly on adult responses, despite the fact that early life stages may be more vulnerable to thermal challenge. Here, we compared the sensitivity of different life history stages of the intertidal gastropod Littorina obtusata using thermal death time curves, which incorporate the intensity and duration of heat stress, and used these to calculate upper critical thermal limits (CTmax) and sensitivity to temperature change (z). Early (larval) life stages had both a lower CTmax and a lower z than adults, suggesting they are less good at withstanding short-term extreme thermal challenges but better able to survive moderate temperatures in the long term. This result supports the predicted trade-off between acute and chronic tolerance to thermal stress, and is consistent with the different thermal challenges that these stages encounter in the intertidal zone. We conclude that different life history stages employ different thermal strategies that may be adaptive. Our findings caution against the use of predictions of the impact of global warming that are based on only adult responses and, hence, which may underestimate vulnerability.

Thermal strategies vary with life history stage.

Studying the altered timing of physiological events during development: it's about time…or is it?

Heterochrony, altered developmental timing between ancestors and their descendents, has been proposed as a pervasive evolutionary feature and recent analytical approaches have confirmed its existence as an evolutionary pattern. Yet, the mechanistic basis for heterochrony remains unclear and, in particular, whether intraspecific variation in the timing of developmental events generates, or has the potential to generate, future between-species differences. Here we make a key step in linking heterochrony at the inter- and intraspecific level by reporting an association between interindividual variation in both the absolute and relative timing (position within the sequence of developmental events) of key embryonic developmental events and genetic distance for the pond snail, Radix balthica. We report significant differences in the genetic distance of individuals exhibiting different levels of dissimilarity in their absolute and relative timing of developmental events such as spinning activity, eyespot formation, heart ontogeny, and hatching. This relationship between genetic and developmental dissimilarity is consistent with there being a genetic basis for variation in developmental timing and so suggests that intraspecific heterochrony could provide the raw material for natural selection to produce speciation.

A genetic basis for intraspecific differences in developmental timing

Climate change is predicted to increase sea level and cause saline intrusion of coastal freshwaters. This will have consequences for freshwater organisms inhabiting such areas; devel- opmental phenotypic plasticity may facilitate the persistence of freshwater species under such scenarios of increased salinity. Here we investigated developmental plasticity under different salin- ity treatments (S = 2, 5, 7 and 9, with artificial pond water (APW) and deionised water (S = 0) as con- trols) in embryos from an upper-estuarine population of the gastropod Radix balthica. We focused on plasticity in the timing of developmental events (heterokairy) at different salinities, including the time of onset (relative and absolute) of 10 developmental events and duration of 4 developmental stages; we also assessed whether salinity affected hatchling morphology and embryonic cardiac activity. There were significant differences in the absolute time of onset of several events with increased salinity, including a delayed first heartbeat in S5 and S7 compared with APW and in the relative time of onset of eye spot formation, first heartbeat and foot attachment between treatments. Stage duration also varied between salinity treatments: the hippo developmental stage lasted signif- icantly longer in S7 compared with APW and development overall was prolonged in S7, with embryos in S9 not developing past the trochophore stage. Salinity also affected both shell size and shell shape of hatchlings. Hence salinity influences the time of onset (absolute and relative) of devel- opmental events and duration of several developmental stages and the morphology of hatchling snails, although the mechanistic basis and fitness implications are, as yet, unknown.

/pdf/salinity-induced-heterokairy-in-an-upper-estuarine-4tjo2zqyeq.pdf

Oliver Tills

Papers

An annotated draft genome for Radix auricularia (Gastropoda, Mollusca).

Thermal strategies vary with life history stage.

Studying the altered timing of physiological events during development: it's about time…or is it?

A genetic basis for intraspecific differences in developmental timing

Salinity-induced heterokairy in an upper-estuarine population of the snail Radix balthica (Mollusca: Pulmonata)