The genetic architecture underlying prey-dependent performance in a microbial predator

Natural selection should favour generalist predators that outperform specialists across all prey types. Two genetic solutions could explain why intraspecific variation in predatory performance is, nonetheless, widespread: mutations beneficial on one prey type are costly on another (antagonistic pleiotropy), or mutational effects are prey-specific, which weakens selection, allowing variation to persist (relaxed selection). To understand the relative importance of these alternatives, we characterised natural variation in predatory performance in the microbial predator Dictyostelium discoideum. We found widespread nontransitive differences among strains in predatory success across different bacterial prey, which can facilitate stain coexistence in multi-prey environments. To understand the genetic basis, we developed methods for high throughput experimental evolution on different prey (REMI-seq). Most mutations (~77%) had prey-specific effects, with very few (~4%) showing antagonistic pleiotropy. This highlights the potential for prey-specific effects to dilute selection, which would inhibit the purging of variation and prevent the emergence of an optimal generalist predator.

Translational Geroscience: Human Models of Healthy Aging and Longevity

While insulin like growth factor-1 (IGF-1) is a well-established modulator of aging and longevity in model organisms, its role in humans is less well understood. Previous ambiguities in part have been attributed to cohort characteristics and unawareness of interactions between age and IGF-1. Centenarians have emerged as an ideal model of healthy aging because they delay the onset of age-related diseases and often remain disease free for the duration of their lifespan. In cohorts of centenarians and generally healthy older adults, we demonstrated that reduced IGF-1 is associated with extended lifespan and health-span. Additionally, we confirmed that IGF-1 interacts with age to modify risk in a manner consistent with antagonistic pleiotropy: younger individuals with high IGF-1 are protected from dementia, vascular disease, diabetes, cancer, and osteoporosis, while older individuals do not exhibit IGF-1-associated protection from disease. These findings offer evidence for IGF-1 modulating health-span and lifespan in humans.

Balancing quality and quantity of social relationships in volatile social environments

Cooperative interactions do not occur in a vacuum, but develop over time in social groups that undergo demographic changes. Intuition suggests that stable social environments might favour individuals that develop few but strong reciprocal relationships (a 'focused' strategy), while volatile social environments do the opposite and favour individuals with more but weaker social relationships (a 'diversifying' strategy). We model reciprocal investments under a tradeoff between quantity and quality of social relationships, and reveal that this intuition is fallible. We find that volatile social environments particularly favour a focused cooperative strategy. This result can be explained by applying the theory of antagonistic pleiotropy, originally developed for senescence, to cooperative strategies. Diversifying social investments benefits late-life individuals that already have their social network built up, but is detrimental early in life when networks must be built from scratch. Under volatile social environments, the age structure of a population remains generally young, and this emphasizes strategies that do well early in life: a focused strategy which makes the individual form its first few social bonds happen quickly. Overall, our model highlights the importance of pleiotropy and population age structure for the evolution of cooperative strategies and other social traits.

Mapping of genotype-by-environment interactions in phenology identifies two cues for flowering in switchgrass (Panicum virgatum)

Plant phenological timings are major fitness components affected by multiple environmental cues; thus, phenological traits can have important genotype-by-environment interactions (GxE). We use a flexible, data-driven method to characterize GxE in the timing of vegetative growth ('green-up') and flowering across eight environments and in two highly divergent switchgrass (Panicum virgatum) populations. We classified polygenic GxE patterns as suggestive of modulation of genetic effects via weather-based cues-or other, unknown modulators. >26% of Gulf population SNPs affecting flowering had effects that covaried with photoperiodicity and >34% of Midwest upland population SNPs affecting flowering had effects that covaried with cumulative growing degree days. 76% of SNP effects on green-up showed antagonistic pleiotropy, a change in effect sign, between environments native to Gulf plants (Texas) and environments native to Midwest plants (North). In contrast, <2% of flowering effects showed antagonistic pleiotropy; the majority (>64%) showed no GxE. Top GxE-associated SNPs were highly enriched in the top associations from an independent pseudo-F2 cross of individuals from the same two populations. Breeding for particular alleles at GxE-associated loci could change flowering responsiveness to photoperiod cues in switchgrass. More broadly, this approach could be used to flexibly characterize patterns of GxE across species, populations and environments.