The Missing Response to Selection in the Wild

Although there are many examples of contemporary directional selection, evidence for responses to selection that match predictions are often missing in quantitative genetic studies of wild populations. This is despite the presence of genetic variation and selection pressures-theoretical prerequisites for the response to selection. This conundrum can be explained by statistical issues with accurate parameter estimation, and by biological mechanisms that interfere with the response to selection. These biological mechanisms can accelerate or constrain this response. These mechanisms are generally studied independently but might act simultaneously. We therefore integrated these mechanisms to explore their potential combined effect. This has implications for explaining the apparent evolutionary stasis of wild populations and the conservation of wildlife. Our Ability to Predict the Response to Selection in the Wild Is Limited Evidence for contemporary microevolution by natural selection has repeatedly been found in both plant and animal populations [1]. However, responses to selection often do not match quantitative genetic expectations in long-term surveys of wild populations (hereafter referred to as surveyed populations) [2], even with 10-70 years of phenotypic and pedigree data [3]. A lack of observed response to selection ('evolutionary stasis') appears to be the norm rather than the exception in these studies [4,5]. This is puzzling because the response to selection was often missing, even though there was evidence for genetic variation and selection pressures on a trait-theoretical prerequisites for evolution by natural selection. These findings reveal a conundrum in which the general expectation of an absence of response to selection derived from studies of these surveyed populations conflicts with the expectation of the presence of a response based on evidence from other types of studies. We first summarize statistical explanations for this conundrum, namely that the measures of selection and quantitative genetic parameters are imprecise. In our opinion, the statistical issues that we highlight below should be taken into account more often in studies of surveyed populations. Our focus is on issues that are most relevant to a mixed modeling approach because this is the most widely used method for estimating quantitative genetic parameters [e.g., additive genetic(co)variance] in surveyed populations. We then briefly discuss the alternative, but not mutually exclusive, role of biological explanations in explaining this conundrum. Biological mechanisms have the potential to impede selection and thereby avoid the erosion of genetic variability by selection. We also introduce mechanisms that we argue need to be taken into account in surveyed populations. Highlights Recent discoveries at the intersection of quantitative genetics and evolutionary ecology are challenging our views on the potential of wild populations to respond to selection. Multiple biological mechanisms can disconnect genetic variation from the response to selection in the wild. We highlight areas for future research. We provide an integrative framework that can be used to qualitatively assess the combined influence of these mechanisms on the response to selection.