Research

Recent evolutionary radiations such as Darwin’s finches, East African cichlids or Heliconius butterflies have served as model systems to understand how novel variation and new species arise. These systems, clearly in the early stages of divergence, have stimulated research into the behavioral, ecological, and genetic bases of reproductive isolation that have arguably transformed our understanding of the origins of biodiversity. However, no analogous classic radiation comes to mind in the largest ecosystem on earth, the ocean. The overarching goal of our research is to develop the hamlets (Hypoplectrus spp, Serranidae, photographs below), simultaneously hermaphroditic reef fishes from the wider Caribbean, into a model system for the study of marine speciation.

The hamlets are diverse, with a variety of color patterns and geographic distributions that provide the opportunity to repeat comparisons both taxonomically and geographically. They encapsulate the entire spectrum of divergence, from genomic similarity to well-diverged species. Mate choice and spawning can be directly observed in the field throughout the year, providing a handle on reproductive isolation which surpasses nearly any other marine group for the sheer number and quality of behavioral observations that can be made in natural populations. Color pattern has been identified as an important ecological trait that is also used for mate choice, and specific hypotheses regarding the role played by natural and sexual selection in speciation have been developed. Finally, a number of genomic resources are available for the group.

Interests

  • Marine speciation
  • Local adaptation
  • Sexual selection
  • Recombination
  • Dispersal
  • Genomics
  • Behavior
  • Theory

Ongoing projects

  • Genomic architecture of speciation

    With the advent of second and third generation DNA sequencing technologies, we have entered a new phase of biological exploration in which natural populations can be assayed for the genomic signatures of speciation, providing the opportunity to identify the patterns and processes leading to genomic divergence. We are assembling a chromosome-level reference genome for Hypoplectrus and resequencing full genomes to address the following questions: (i) What is the genomic architecture of speciation, and how does it evolve along the speciation continuum? (ii) What are the genomic elements underlying species differences, and do their evolutionary history differ from the rest of the genome? (iii) How repeatable are patterns of genomic divergence? (iv) Does speciation proceed in the presence of gene flow? Led by Kosmas Hench, funded by the DFG, Smithsonian Institute for Biodiversity Genomics and Global Genome Initiative.

  • Animal personality and speciation

    Recent efforts aimed at rethinking speciation research have pointed out the need to integrate emerging fields, break down polarized categories and include potentially overlooked avenues of research such as the role played by animal personality. There is growing theoretical interest in the evolutionary implications of animal personality, but empirical studies are lagging behind. We are doing long-term observations of tagged individuals in natural populations to identify personality traits in butter hamlets (Hypoplectrus unicolor) and explore whether and how such traits may be linked to reproductive isolation. Led by Sophie Picq, funded by IMPRS through GEOMAR and a short-term fellowship from the Smithsonian Tropical Research Institute.

  • Evolution of egg trading

    Hermaphroditism is estimated to occur in about 65,000 animal species distributed over 70% of animal phyla, which represents a third of animal species excluding insects. A significant proportion of hermaphrodites are simultaneous hermaphrodites, which sets the stage for self-fertilization and egg trading, whereby individuals reciprocally fertilize each other’s eggs. Egg trading is of particular interest because it has been suggested to represent a rare case of cooperation among unrelated individuals and to stabilize simultaneous hermaphroditism. Nevertheless, egg trading remains a rarity among simultaneous hermaphrodites, having been reported in a restricted number of polychaete, sea slug and fish species only. While previous studies have addressed the stability of egg trading once established, how it may initially invade a population of non-trading simultaneous hermaphrodites remains an open question. Here, we tackle this problem with an analytical model that considers explicitly encounter rates and costs of egg production in a population that may include non-traders (who provide eggs at every mating opportunity), traders (who provide eggs only if their partners also do so) and cheaters (who never provide eggs and only mate in the male role). Led by Jorge Peña in collaboration with Dr. Georg Nöldeke, funded by The Future Ocean.

  • Genomic architecture of local adaptation

    Whether populations are adapted to local conditions, and if so through what mechanisms, are fundamental questions in evolutionary ecology. This is particularly true in the marine environment, where absolute barriers to the movement of organisms are few and planktonic larval stages provide potential for extensive dispersal. Are marine populations able to adapt to local environmental conditions in such a potentially high gene-flow context? This is not only a basic question but also an applied one, as the occurrence of locally adapted marine populations has far-reaching implications for management, conservation, and the ability to cope with global change. We are resequencing hamlet genomes from a variety of locations across the wider Caribbean to address this question. Led by O. Puebla, funded by the lab.

  • Color patterns in coral reef fishes

    The colors patterns displayed by coral reef fishes are among the most visually stunning traits in animals, but they are notoriously difficult to analyze and quantify objectively. Using the hamlets as a model system, we are developing a pipeline to quantify both color and patterns in coral reef fishes. This project involves fieldwork, high-resolution photography, spectrophotometry, image analysis as well as a citizen science component whereby scuba divers are invited to send us their hamlet photographs. Led by Derya Akkaynak and Kosmas Hench, funded by The Future Ocean and GEOMAR.

  • Matching theory, mutual mate choice and speciation

    The award of the 2012 Nobel Prize in Economic Sciences to the two main founders of matching theory, Alvin E. Roth and Lloyd S. Shapley, establishes the fundamental importance and specificity of this theoretical framework. In evolutionary biology, matching theory provides a very distinctive opportunity to address sexual selection and speciation in a context of mutual mate choice. We are using matching theory to explore the role played by mutual mate choice in speciation. Led by Sophie Picq, funded by IMPRS through GEOMAR.

  • Hamlet community dynamics

    The hamlets constitute a distinctive marine model system for the study of a variety of ecological and evolutionary processes including egg trading, sexual selection and speciation. Temporal changes in hamlet communities can potentially affect or be affected by such processes, but the dynamics of hamlet communities and their ecological drivers are still eluding ecologists. Reasons for this knowledge gap include the difficulty to identify some individuals due to extensive color pattern variation in the group, their relatively low densities and the paucity of detailed hamlet community surveys. The hamlets from La Parguera, Puerto Rico, constitute a notable exception with a thorough survey by Aguilar-Perera available for the year 2000. In this project, we leverage this opportunity to test whether hamlet communities are temporally stable. Seventeen years later we revisited the same reefs and conducted transect surveys covering 14,000 m2 across 16 reefs complemented with standardized in situ photographs of live specimen of all species and color pattern variants found using a new pipeline specifically developed for this purpose. Led by Kosmas Hench, funded by the lab.

  • Maya hamlet conservation genomics

    The recently described Maya hamlet (Hypoplectrus maya), endemic to the coastal lagoon of the Belize Barrier Reef, appears to have severely declined during the last two decades. In this project we leverage full-genome data to reconstruct the evolutionary history of this atypical species and estimate its effective population size. Led by Ben Moran, funded by the National Geographic Society, Northeastern University and DFG.

  • Population genetic structure of western Baltic seatrout

    Seatrout, the anadromous form of the brown trout (Salmo trutta), is among the most targeted species by marine recreational and small-scale coastal commercial fisheries in Germany. Stocking activities of various intensities have been conducted for more than a century, yet close to nothing is known about the population genetic structure of German seatrout. This knowledge is essential for the design of stocking programs that conserve the genetic integrity and potential for local adaption of seatrout populations. This is particularly true in the German state of Schleswig-Holstein where short distances separate watersheds flowing into the Baltic and North Seas, where a potential migration corridor was created 120 years ago with the opening of the Kiel Canal, and where historic records indicate that fishes of both North Sea and Baltic Sea origin have been used to stock Baltic Sea rivers. We are surveying populations from the Baltic Sea, Kiel Canal and North Sea rivers using a panel of high-quality SNP markers. Led by Christoph Petereit.

Past projects

  • Recombination in the eggs and sperm

    When there is no recombination in one sex, it is the in the heterogametic one. This observation is so consistent that it constitutes one of the few patterns that may be regarded as a ‘rule’ or a ‘law’ in biology, and Haldane proposed that it may driven by selection against recombination in the sex chromosomes. Nevertheless, differences in recombination rate between the sexes have also been reported in hermaphroditic species that lack sex chromosomes, and an alternative explanation is required in this case. In plants—the vast majority of which are hermaphroditic—selection at the haploid stage has been proposed to drive heterochiasmy. Yet few data are available for hermaphroditic animals, and barely any for hermaphroditic vertebrates. We are using reciprocal crosses between two black hamlets (Hypoplectrus nigricans, Serranidae), simultaneously hermaphroditic reef fishes from the wider Caribbean, to generate high-density egg- and sperm-specific linkage maps for each parent. Led by Loukas Theodosiou, funded by IMPRS and the Smithsonian Tropical Research Institute.