Embryonic gene expression among pollutant resistant and sensitive Fundulus heteroclitus populations

Abstract

Changes in gene expression, coupled with biochemical, physiological, and behavioral alterations, play a critical role in adaptation to environmental stress. Our goal was to explore ways natural populations may have adapted to local, polluted environments. We took advantage of natural populations of Fundulus heteroclitus, one of the few studied fish species in North America that has established resistant populations in highly contaminated urban estuaries. We analyzed morphology, physiology, and gene expression of developing F. heteroclitus embryos during late organogenesis (stage 31); these embryos were from both resistant and sensitive populations and were raised in a common, unpolluted environment. While cardiac heart rates show significant differences between embryos of parents from clean and heavily contaminated Superfund sites, time-to-stage, embryo morphology, and gene expression profile analyses do not differ significantly between untreated embryos from resistant and sensitive populations. Further evaluation that includes tissue-specific approaches in gene expression analysis and larger sample sizes may be necessary to highlight important phenotypes associated with mechanisms of sensitivity and resistance among natural F. heteroclitus embryo populations. Alternatively, population differences may be masked by developmental canalization, and biologically important differences between sensitive and resistant embryos may only manifest with exposure (e.g., be dependent on gene by environment interactions).

When evolution is the solution to pollution: Key principles, and lessons from rapid repeated adaptation of killifish (Fundulus heteroclitus) populations

“…Application of the next generation of genomewide microarray tools revealed striking differences in pollutant responses between tolerant and sensitive populations, particularly during early life, and striking parallelism among tolerant populations. Almost no differences in constitutive gene expression were apparent between tolerant and sensitive populations during development in clean, “common‐garden” conditions (Bozinovic & Oleksiak, 2010). However, upon exposure to model toxicants, including PCBs and PAHs, large differences in inducible expression clearly distinguished tolerant fish from fish from a nearby sensitive reference population (Bozinovic et al., 2013; Oleksiak et al., 2011; Whitehead et al., 2010).…”

Common mechanism underlies repeated evolution of extreme pollution tolerance

“…This pattern does not support unique evolved responses for each tolerant population, but rather is consistent with the hypothesis that tolerant populations converged on a heritable, common, non-neutral and putatively adaptive functional response to a shared evolutionary challenge. Importantly, constitutive differences in gene expression in a static common-garden do not reveal mechanisms of adaptive divergence in killifish populations [19] probably as a result of developmental canalization, whereas challenge with a model pollutant is necessary to reveal adaptive population divergence in the genomic response function (figure 3).…”

Genomic approaches with natural fish populations from polluted environments

“…This study used a larger array representing approximately 7,000 unique expressed sequence tag clusters. In surprising contrast to the large number of differentially expressed genes found in the adult studies, no genes were differentially expressed between embryos from polluted and reference populations [25]. This lack of difference in gene expression in a common garden environment suggests that gene expression is canalized during development and that gene by environment interactions may be necessary to clarify differences among embryos from polluted and reference populations.…”