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Unique maternal and environmental effects on the body morphology of the Least Killifish, Heterandria formosa.

ABSTRACT: An important step in diagnosing local adaptation is the demonstration that phenotypic variation among populations is at least in part genetically based. To do this, many methods experimentally minimize the environmental effect on the phenotype to elucidate the genetic effect. Minimizing the environmental effect often includes reducing possible environmental maternal effects. However, maternal effects can be an important factor in patterns of local adaptation as well as adaptive plasticity. Here, we report the results of an experiment with males from two populations of the poeciliid fish, Heterandria formosa, designed to examine the relative influence of environmental maternal effects and environmental effects experienced during growth and development on body morphology, and, in addition, whether the balance among those effects is unique to each population. We used a factorial design that varied thermal environment and water chemistry experienced by mothers and thermal environment and water chemistry experienced by offspring. We found substantial differences between the two populations in their maternal and offspring norms of reaction of male body morphology to differences in thermal environment and water chemistry. We also found that the balance between maternal effects and postparturition environmental effects differed from one thermal regime to another and among traits. These results indicate that environmental maternal effects can be decidedly population-specific and, as a result, might either contribute to the appearance of or blur evidence for local adaptation. These results also suggest that local adaptation might also occur through the evolution of maternal norms of reaction to important, and varying, environmental factors.

SUBMITTER: Landy JA

PROVIDER: S-EPMC6024122 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Unique maternal and environmental effects on the body morphology of the Least Killifish, <i>Heterandria formosa</i>.

Landy J Alex JA Travis Joseph J

Ecology and evolution 20180524 12

An important step in diagnosing local adaptation is the demonstration that phenotypic variation among populations is at least in part genetically based. To do this, many methods experimentally minimize the environmental effect on the phenotype to elucidate the genetic effect. Minimizing the environmental effect often includes reducing possible environmental maternal effects. However, maternal effects can be an important factor in patterns of local adaptation as well as adaptive plasticity. Here, ...[more]

PMID: 29988417

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Project description:Populations with different densities often show genetically based differences in life histories. The divergent life histories could be driven by several agents of selection, one of which is variation in per-capita food levels. Its relationship with population density is complex, as it depends on overall food availability, individual metabolic demand, and food-independent factors potentially affecting density, such as predation intensity. Here, we present a case study of two populations of a small live-bearing freshwater fish, one characterized by high density, low predation risk, low overall food availability, and presumably low per-capita food levels, and the other by low density, high predation risk, high overall food availability, and presumably high per-capita food levels. Using a laboratory experiment, we examined whether fish from these populations respond differently to food limitation, and whether size at birth, a key trait with respect to density variation in this species, is associated with any such differential responses. While at the lower food level growth was slower, body size smaller, maturation delayed, and survival reduced in both populations, these fitness costs were smaller in fish from the high-density population. At low food, only 15% of high-density fish died, compared to 75% of low-density fish. This difference was much smaller at high food (0% vs. 15% mortality). The increased survival of high-density fish may, at least partly, be due to their larger size at birth. Moreover, being larger at birth enabled fish to mature relatively early even at the lower food level. We demonstrate that sensitivities to food limitation differ between study populations, consistent with selection for a greater ability to tolerate low per-capita food availability in the high-density population. While we cannot preclude other agents of selection from operating in these populations simultaneously, our results suggest that variation in per-capita food levels is one of those agents.

Project description:BACKGROUND:Climatic and sea-level fluctuations throughout the last Pleistocene glacial cycle (~130-0 ka) profoundly influenced present-day distributions and genetic diversity of Northern Hemisphere biotas by forcing range contractions in many species during the glacial advance and allowing expansion following glacial retreat ('expansion-contraction' model). Evidence for such range dynamics and refugia in the unglaciated Gulf-Atlantic Coastal Plain stems largely from terrestrial species, and aquatic species Pleistocene responses remain relatively uninvestigated. Heterandria formosa, a wide-ranging regional endemic, presents an ideal system to test the expansion-contraction model within this biota. By integrating ecological niche modeling and phylogeography, we infer the Pleistocene history of this livebearing fish (Poeciliidae) and test for several predicted distributional and genetic effects of the last glaciation. RESULTS:Paleoclimatic models predicted range contraction to a single southwest Florida peninsula refugium during the Last Glacial Maximum, followed by northward expansion. We inferred spatial-population subdivision into four groups that reflect genetic barriers outside this refuge. Several other features of the genetic data were consistent with predictions derived from an expansion-contraction model: limited intraspecific divergence (e.g. mean mtDNA p-distance = 0.66%); a pattern of mtDNA diversity (mean Hd = 0.934; mean ? = 0.007) consistent with rapid, recent population expansion; a lack of mtDNA isolation-by-distance; and clinal variation in allozyme diversity with higher diversity at lower latitudes near the predicted refugium. Statistical tests of mismatch distributions and coalescent simulations of the gene tree lent greater support to a scenario of post-glacial expansion and diversification from a single refugium than to any other model examined (e.g. multiple-refugia scenarios). CONCLUSIONS:Congruent results from diverse data indicate H. formosa fits the classic Pleistocene expansion-contraction model, even as the genetic data suggest additional ecological influences on population structure. While evidence for Plio-Pleistocene Gulf Coast vicariance is well described for many freshwater species presently codistributed with H. formosa, this species demography and diversification departs notably from this pattern. Species-specific expansion-contraction dynamics may therefore have figured more prominently in shaping Coastal Plain evolutionary history than previously thought. Our findings bolster growing appreciation for the complexity of phylogeographical structuring within North America's southern refugia, including responses of Coastal Plain freshwater biota to Pleistocene climatic fluctuations.

Project description:BackgroundWe aimed to examine maternal metabolic correlates of neonate body composition, and the potential mediating effect of the placenta.MethodsData were collected throughout pregnancy and at delivery. An oral glucose tolerance test (OGTT) was conducted in order to diagnose or rule out gestational diabetes mellitus (GDM). Maternal weight and blood pressure were taken and hypertension and gestational weight gain (GWG) were defined. Gestational age, birth weight (BW) and weight to length ration (WLR) were recorded. Photographs were taken of the placenta, and the widths and lengths were measured digitally. Body composition was analysed via air displacement plethysmography or dual-energy x-ray absorptiometry. Mediation models were conducted to determine the mediation effect of the placental variables on the relationships between maternal health variables and neonate outcomes. Next, interaction terms were added to models to determine how maternal and placental variables interacted in their effect on neonate outcomes.ResultsA total of n = 280 women were included in the analysis. Majority were overweight or obese. Fourteen percent of women developed GDM during pregnancy, 5% had hypertension during pregnancy, 32% were HIV positive, and 32% had anemia. For the birth weight outcome, coefficients of BMI were attenuated by the addition of placental variables (Model 1 β=18.66 vs Model 2 β=16.40). Similar patterns were evident for GWG and hypertension, and for the WLR outcome. In all cases the addition of the placental variables attenuated associations between maternal exposures and neonatal outcomes, yet the level of significance did not change. Inclusion of interaction terms reversed the direction of the relationships between hypertension and BW and WLR, and between GWG and WLR.ConclusionThe placenta buffers some harmful effects of obesity, GWG, and hypertension on neonate size, and placental efficiency interacted with most maternal risk factors to either counteract, or attenuate relationships with neonate size at birth. However the placenta was unable to completely counteract the negative effect of excess nutrient supply on in utero growth.

Dataset Information

Unique maternal and environmental effects on the body morphology of the Least Killifish, Heterandria formosa.

Publications

Unique maternal and environmental effects on the body morphology of the Least Killifish, <i>Heterandria formosa</i>.

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