LAUSR

Ecological and environmental factors are critical determinants of developmental outcome, and there is a growing interest in the mechanisms that integrate these extrinsic factors into intrinsic developmental programs. Perhaps more important, there is real need to understand the ecological and evolutionary consequences of altered developmental outcomes, especially in the context of climate change. In order to study extrinsic factors that alter developmental programs, it is essential to work with organisms in an environmentally and ecologically relevant context. The standard developmental “model organisms” are not always the best choice for these studies due to a variety of factors that include their own natural history and the historic focus on choosing models that develop quickly, are easily reared in the lab, and are amenable to genetic manipulation. Thus, there is a growing need to expand our focus in developmental studies to organisms that are tractable for laboratory studies, but that also have a life history and environmental context that is relevant to the scientific questions we wish to answer. Recent technological advances have removed many of the barriers to working with organisms outside of the “chosen few” model organisms, and this is changing the landscape of developmental biology research. This special issue titled “Annual Killifishes as Model Systems for Advancing Understanding of Evolution and Developmental Biology” is focused on highlighting the utility of annual killifishes for studies of ecological and environmental developmental biology. Annual killifishes have evolved a unique life history that includes the ability to arrest development at up to three stages of embryonic diapause, altered cell migrations associated with early development and gastrulation, and rapid aging. In addition, they have the ability to actively develop in the face of highly variable and often extreme environmental conditions that most species cannot endure, or that would lead to abnormal developmental outcomes. Their embryos are also known to respond to ecological and environmental cues that can alter entrance into diapause. Finally, the natural history of these species provides an opportunity to study multiple lineages that are thought to have independently evolved the complex suite of characters that define annual killifishes. Thus, from many perspectives this group of fishes provides an unparalleled opportunity to study the evolution of complex developmental traits, alternative developmental phenotypes, and tolerance to environmental stress in vertebrate embryos. Further, their unique biology easily captures the interest and imagination of learners at all levels of education and thus can be used to illustrate difficult concepts such as adaptation and evolution to a broad audience. In this issue, Berois et al. review the unique life history of annual killifishes and highlight the growing global community of researchers that are have chosen to study these fascinating fishes. Martin and Podrabsky focus on defining the various types of developmental arrest that are possible in annual killifishes and their relatives in an attempt to clarify these distinct types of dormancy and their potential importance. From a developmental perspective, Pereiro et al. describe events associated with gastrulation in species of Austrolebias, the first detailed report of gastrulation events in any annual killifish. Podrabsky et al. also offer an updated set of standardized stages for annual killifishes using Austrofundulus limnaeus as model. The ecological aspects of development in annual killifishes are highlighted by a number of articles. First, Arezo et al. explore how presence of adult fish and environmental temperature can induce two different diapause I phenotypes in species of Austrolebias from Uruguay. Vrtilek et al. document an uncoupling of maternal energetic investment from duration of development in embryos of the genus Nothobranchius from Mozambique. Reichard et al. explore hatching variation in wild populations of Nothobranchius in relation to pond inundation and bet-hedging strategies for survival in unpredictable environments. Finally, Dominguez-Castanedo et al. explore the ecological relevance of the three different diapause stages in Millerichthys robustus, the only annual killifish from North America. Together, this group of articles highlights the unique biology of annual killifishes, and how this can be leveraged to better understand the ecological, environmental, and evolutionary aspects of vertebrate development. Our hope is that this issue sparks interest in annual killifishes among other biologists that leads to a growth in the global community of researchers who can leverage these models to better understand how ecological and environmental factors are integrated into vertebrate developmental programs, and to realize the long-term consequences of these altered developmental outcomes.