BIODIVERSITY DISCOVERY AND DIVERSIFICATION
Widespread habitat destruction and deterioration coupled with global climate change are resulting in the unprecedented extinction of species at a local and global scale. I strongly feel that the pervasive environmental problems that now define the Anthropocene imply that our efforts to catalog extant biodiversity and understand the processes generating it need to be prioritized. Our laboratory actively engage in biodiversity discovery. As importantly, we aim to understand the processes generating this diversity.
Interestingly, genetic diversification does not always correlate with phenotypic dissimilarity, resulting in cryptic species pairs or complexes. Furthermore, phenotypic plasticity can result in remarkable phenotypic dissimilarity in spite of genetic homogeneity. The above processes certainly pose a major challenge for biodiversity cataloging and have profound implications for conservation and evolutionary theory. Our laboratory is currently focusing in testing whether or not species with wide geographic ranges represent complexes of cryptic species. For this purpose, we use available state-of-the-art species delimitation and validation approaches combined with population genetics strategies. We are working with cosmopolitan or species with wide geographic ranges in the Caribbean sea and the Indo Pacific ocean given the great number of species that these regions/provinces harbor. Our approach informs about mechanisms of speciation and diversification.
With regards to diversification, we are interested in testing two most relevant but poorly explored questions in marine biogeography: Is the Caribbean sea a cradle or a museum? Is the North Pacific ocean a Center of Origin or Accumulation for temperate species? Our recent studies using 'peppermint shrimps' belonging to the genus Lysmata indicate that the Caribbean is a cradle, with various speciation events taking place recently (< 3 mya). Additional studies using 'hooded shrimps' belonging to the genera Betaeus and Betaeopsis indicate that North Pacific represents a 'Center of Origin' for marine shallow water temperate species.
Certainly, our laboratory will continue developing this research theme during the next decade. Our results has been published in, among others, Molecular Phylogenetics and Evolution, Marine Biology, Zootaxa, and PLoS ONE.
EVOLUTIONARY BIOLOGY: ADAPTIVE VALUE OF SEX ALLOCATION STRATEGIES
Sex allocation theory is considered a poster-child in evolutionary biology with a remarkable body of literature supporting its main predictions. Sex allocation theory is the body of models that attempts to explain the evolution and adaptive significance of different sexual systems, including mixed gender expression patterns such as protandric simultaneous hermaphroditism (see below). Sex allocation theory is not limited only to predicting those conditions explaining the evolution and stability of particular sexual systems. It also attempts to answer and unify questions such as: (a) when and how should individuals adjust the sex of their offspring in response to environmental conditions? (b) when and in what direction are individuals selected to change sex? and (c) what is the optimal amount of resources that individuals should allocate to male and female reproduction in simultaneous hermaphrodites?
Sex allocation theory, now considered one of the most robust branches of evolutionary biology, has been most useful in predicting and understanding those conditions favoring the evolution of strictly sequential and strictly simultaneous hermaphroditism. However, theoretical studies conducted in an attempt to explain the evolution of mixed sexual systems, such as protandric simultaneous hermaphroditism, still lag behind. One enigmatic example of mixed sexual systems in animals is protandric simultaneous hermaphroditism, in which individuals consistently mature and reproduce initially as males and later in life become functional simultaneous hermaphrodites.
For more than a decade now, our laboratory has been interested in understanding the adaptive value of mixed sexual systems, including protandric simultaneous hermaphroditism, using shrimps belonging to the genus Lysmata as a model system. We use a combination of laboratory experiments and field observations to test hypothetical scenarios expected to favor protandric simultaneous hermaphroditism in these shrimps. Our results are among the first demonstrating that a combination of size-dependent mortality and sex-dependent time commitments explains the adaptive value of this sexual system (see Baeza 2006, 2007, 2013). We also use protandric simultaneous hermaphroditism to test hypotheses at the core of sex allocation theory. For instance, sex allocation theory predicts shifts in the timing of sex phase or sex change in specie with sequential gender expression patterns according to environmental, including social, conditions. Our studies are among a few others demonstrating that male individuals decide to delay 'change sex' in environments in which male mating opportunities are frequent. In turn, in monogamous situations in which male mating opportunities are rare, males quickly turn into simultaneous hermaphrodites. At present, our laboratory is testing for predicted trade-offs between the sex functions and the role of sexual selection in explaining the adaptive value of this sexual system.
Our laboratory will continue developing this research program during the next decades. Our results has been published in, among others, Evolution, Behavioral Ecology and Sociobiology, Coral Reefs, and PLoS ONE.
EVOLUTIONARY BIOLOGY: ADAPTIVE VALUE OF MATING SYSTEMS
Other than sexual strategies, animals, including marine invertebrates, exhibit remarkable disparity in terms of reproductive behaviors and mating tactics, yet the mechanisms driving these tactics are not fully understood. Remarkably, social monogamy (defined as pairs of conspecifics spending extensive periods of time together) has evolved multiple independent times in marine and terrestrial environments among invertebrate and vertebrate organisms that may or may not exhibit parental care. In species with biparental care, the benefits arising from shared parental duties when rearing expensive offspring (both in terms of energy and time) appear to explain its adaptive value. In the absence of biparental care, various other hypotheses have been put forward to explain the adaptive significance of monogamy (e.g., “territorial cooperation” hypothesis; “mate-guarding” hypothesis; among others). Most recently, theoretical considerations predict that social (living together) and genetic (lifelong) monogamy is adaptive in resource-specialist symbiotic invertebrates inhabiting relatively small and morphologically simple hosts in tropical environments where predation risk away from hosts is high. Under the conditions above, movement among refuges is hindered and their monopolization is favored due to refuge scarcity as well as their large value in offering protection against predators. Because spatial limitation allows only a few reproductive individuals to cohabit the same refuge, both males and females are expected to maximize their reproductive success by sharing 'their' dwelling with a member of the opposite sex.
Our laboratory actively explores the adaptive value of social monogamy in symbiotic invertebrates. We use a combination of field observations as well as laboratory and field experiments to test theoretical frameworks predicting the adaptive value of monogamy. Our results suggest that social and in many cases genetic monogamy is adaptive in environments in which predation risk off refuges severely constraint roaming by male individuals. On the other hand, some of our studies have also found non-monogamous and putatively promiscuous symbiotic species inhabiting environments that should favor monogamy! Currently, we are trying to understand what other intrinsic (e.g., female receptivity) and extrinsic (e.g., inter-specific competition) conditions favor or constraint this fascinating reproductive strategy. Furthermore, we are using manipulative experiments to test the role of sexual conflict, a rarely explored procces, in driving male and female sexual behavior and mating interactions.
Our results has been published in, among others, Journal of Zoology, Coral Reefs, Marine Biology, Marine Ecology, and PLoS ONE.
SEASCAPE GENOMICS: CONNECTIVITY IN THE GREATER CARIBBEAN SEA
We are excited about this new research program that will continue developing during the next decades. Exploring genetic structure and biophysical connectivity among conspecific populations is an important exercise for understanding the mechanisms driving species distribution, for the proper management of exploited resources, for guiding sound conservation strategies, and ultimately, for illuminating evolutionary processes. In marine systems, organisms were long thought to exhibit high population connectivity, high gene flow, and subsequent low population genetic structure. This assumption was based on the perception that geographical barriers are less obvious in marine, as opposed to terrestrial, environments. Thus, oceanic currents were expected to favor (rather than limit) inter-population connectivity and thus, promote genetic homogenization over large spatial scales. Further, many marine organisms disperse during extended larval periods (compared to terrestrial species) and occupy wide geographical ranges; and thus, marine species were expected to have considerable long-distance dispersal ability also favoring genetic homogenization across large spatial scales. Active research in this topic over more than 40 years has provided, however, limited support for the view of high levels of contemporary gene flow and low genetic differentiation among populations of marine organisms. For instance, some studies have reported remarkable levels of genetic differentiation among populations in species with considerable dispersal ability, and yet, little to no genetic population differentiation occurs in some species with large geographic ranges and larval periods.
In the marine realm, conditions that potentially drive connectivity among populations can be divided into intrinsic and extrinsic factors. Extrinsic conditions include, among others, geographic distance among populations (i.e., isolation by distance), local adaptation processes, and oceanographic phenomena that can favor (or reduce) gene flow among populations. Intrinsic conditions include biological traits such as mode of development, duration of the pelagic larval period in species with indirect development, larval behaviors, and generation times, among others. Among the above, the mode of larval development and the duration of the pelagic larval period appear to be of utmost importance in driving population connectivity. The relative importance of intrinsic and extrinsic conditions in shaping genomic seascape patterns remains unresolved.
Our laboratory is currently using next generation sequencing technologies to determine population connectivity patterns for the spiny lobster Panulirus argus across the greater Caribbean region, including the Florida Keys in the north and Venezuela in the south. We have selected as a model system the Caribbean spiny lobster considering that this species is the target of the most socio-economically important fishery in the greater Caribbean region and plays a pivotal ecological role as prey and predator in coral reefs. All Caribbean populations of the spiny lobster are either over-exploited or fully exploited, landings since 2000 have been 20 – 30% below historical levels, and fishing pressure is expected to increase during the next decade given the current economic development in the entire region. The extraction of lobsters in Florida is highly efficient: more than 90-95% of the standing stock is extracted every year. Replenishment of this northern population occurs every year via 'seeding' of long-lived floating larvae that can originate as south as Colombia/Venezuela and travel for months with marine currents to finally settle around Florida. Determining which Caribbean populations act as 'sources' is a matter of food security for the USA and examination of fine-scale population connectivity in the region, only possible via genomic technology, is of utmost importance to establish an international network of marine reserves, which can concomitantly serve as biodiversity refugia with the Caribbean spiny lobster as the 'umbrella' species. Furthermore, studying connectivity patterns in this species will improve our understanding of evolutionary processes in the greater Caribbean region, a biodiversity hot-spot affected by both environmental change and local stressors. Please, stay tuned for news. The first genomic resources we have developed will be published in the near future!
CONSERVATION AND RESOURCES: ORNAMENTAL FISHERIES
Ornamental organisms support a multi-million dollar global industry that provides marine and freshwater aquarist with an assortment of over 1400 species of invertebrates, vertebrates, plants, and algae. Importantly, many ornamental fisheries operate unnoticed due to their niche market, the frequency of product export, and the small size attained by the target organisms. Although numerous, ornamental fisheries have historically received minor attention from a resource-management standpoint. Furthermore, management of the few regulated ornamental fisheries relies on limited information about the life history of the target species. This marine industry most often depends upon harvesting of organisms from the natural environment. The extraction of ornamentals has intensified remarkably during the last two decades, and this fishing effort likely will continue to increase during the coming years. It is therefore urgent to develop a baseline of biological information so marine ornamental fisheries can be managed sustainability.
One research area that has turned increasingly relevant in our lab is the study of the reproductive biology of heavily traded marine invertebrate in the western Atlantic. Examples include boxer shrimps from the genus Stenopus, true crabs from the species complex Mithrax - Mithraculus, caridean shrimps from the genera Lysmata, Ancylomenes, and Periclimenes, and hermit crabs from the genera, Dardanus, Petrochirus, and Clibanarius. Our goal is that the information we produce will form the baseline for models aimed at assessing the stock condition and sustainability of this heavily harvested ornamental crustaceans.
'MIKE AND THE PEPPERMINTS'
A Life of Learning
A video featuring Mike Dickson's work with peppermint shrimps in SW Florida. This video entitled 'Mike and the Peppermints' (OCYPODE PRODUCTIONS, Director: Mike Crandall) earned a prize in the 'Beneath the Waves' film festival held together with the Benthic Ecology Meeting 2014 in Jacksonville, Florida. Mike is a former student of our collaborator Don Behringer at University of Florida.