Félix Rodríguez

Evidence of size-selective evolution in the fighting conch from prehistoric subsistence harvesting.

Intensive size-selective harvesting can drive evolution of sexual maturity at smaller body size. Conversely, prehistoric, low-intensity subsistence harvesting is not considered an effective agent of size-selective evolution. Uniting archaeological, palaeontological and contemporary material, we show that size at sexual maturity in the edible conch Strombus pugilis declined significantly from pre-human (approx. 7 ka) to prehistoric times (approx. 1 ka) and again to the present day. Size at maturity also fell from early- to late-prehistoric periods, synchronous with an increase in harvesting intensity as other resources became depleted. A consequence of declining size at maturity is that early prehistoric harvesters would have received two-thirds more meat per conch than contemporary harvesters. After exploring the potential effects of selection biases, demographic shifts, environmental change and habitat alteration, these observations collectively implicate prehistoric subsistence harvesting as an agent of size-selective evolution with long-term detrimental consequences. We observe that contemporary populations that are protected from harvesting are slightly larger at maturity, suggesting that halting or even reversing thousands of years of size-selective evolution may be possible.

Molluscan subfossil assemblages reveal the long-term deterioration of coral reef environments in Caribbean Panama

Caribbean reef corals have declined sharply since the 1980s, but the lack of prior baseline data has hindered identification of drivers of change. To assess anthropogenic change in reef environments over the past century, we tracked the composition of subfossil assemblages of bivalve and gastropod mollusks excavated from pits below lagoonal and offshore reefs in Bocas del Toro, Panama. The higher prevalence of (a) infaunal suspension-feeding bivalves and herbivorous and omnivorous gastropods in lagoons and (b) epifaunal and suspension-feeding bivalves and carnivorous and suspension-feeding gastropods offshore reflected the greater influence of land-based nutrients/sediments within lagoons. Temporal changes indicated deteriorating environmental conditions pre-1960 in lagoons and post-1960 offshore, with offshore communities becoming more similar to lagoonal ones since 1960. Relative abundances of dominant bivalve species tracked those of their coral hosts, revealing broader ecosystem effects of coral community change. The nature and timing of changes implicate land-based runoff in reef deterioration.

Comparative anatomy of internal incubational sacs in cupuladriid bryozoans and the evolution of brooding in free-living cheilostomes.

Numerous gross morphological attributes are shared among unrelated free‐living bryozoans revealing convergent evolution associated with functional demands of living on soft sediments. Here, we show that the reproductive structures across free‐living groups evolved convergently. The most prominent convergent traits are the collective reduction of external brood chambers (ovicells) and the acquisition of internal brooding. Anatomical studies of four species from the cheilostome genera Cupuladria and Discoporella (Cupuladriidae) show that these species incubate their embryos in internal brooding sacs located in the coelom of the maternal nonpolymorphic autozooids. This sac consists of a main chamber and a narrow neck communicating to the vestibulum. The distal wall of the vestibulum possesses a cuticular thickening, which may further isolate the brood cavity. The presence of this character in all four species strongly supports grouping Cupuladria and Discoporella in one taxon. Further evidence suggests that the Cupuladriidae may be nested within the Calloporidae. Based on the structure of brooding organs, two scenarios are proposed to explain the evolution of the internal brooding in cupuladriids. The evolution of brood chambers and their origin in other free‐living cheilostomes is discussed. Unlike the vast majority of Neocheilostomina, almost all free‐living cheilostomes possess nonprominent chambers for embryonic incubation, either endozooidal and immersed ovicells or internal brooding sacs, supporting the idea that internal embryonic incubation is derived. We speculate that prominent skeletal brood chambers are disadvantageous to a free‐living mode of life that demands easy movement through sediment in instable sea‐floor settings. J. Morphol., 2009.

Neogene Proto-Caribbean porcupinefishes (Diodontidae)

Fossil Diodontidae in Tropical America consist mostly of isolated and fused beak-like jawbones, and tooth plate batteries. These durophagous fishes are powerful shell-crushing predators on shallow water invertebrate faunas from Neogene tropical carbonate bottom, rocky reefs and surrounding flats. We use an ontogenetic series of high-resolution micro CT of fossil and extant species to recognize external and internal morphologic characters of jaws and tooth plate batteries. We compare similar sizes of jaws and/or tooth-plates from both extant and extinct species. Here, we describe three new fossil species including †Chilomycterus exspectatus n. sp. and †Chilomycterus tyleri n. sp. from the late Miocene Gatun Formation in Panama, and †Diodon serratus n. sp. from the middle Miocene Socorro Formation in Venezuela. Fossil Diodontidae review included specimens from the Neogene Basins of the Proto-Caribbean (Brazil: Pirabas Formation; Colombia: Jimol Formation, Panama: Gatun and Tuira formations; Venezuela: Socorro and Cantaure formations). Diodon is present in both the Atlantic and Pacific oceans, whereas the distribution of Chilomycterus is highly asymmetrical with only one species in the Pacific. It seems that Diodon was as abundant in the Caribbean/Western Atlantic during the Miocene as it is there today. We analyze the paleogeographic distribution of the porcupinefishes group in Tropical America, after the complete exhumation of the Panamanian isthmus during the Pliocene.

Embryonic brooding and clonal propagation in tropical eastern Pacific cupuladriid bryozoans

Colonial invertebrates often mix sexual and asexual methods of propagation, and a comprehensive understanding of both is required for life history study. The asexual cloning of new colonies in cupuladriid bryozoans is much better studied than the formation of new colonies by sexual reproduction. As such, the relative investments of sexual and asexual modes of propagation remain uncertain. This preliminary study explores patterns of embryonic brooding as a measure of investment into sexual reproduction. We conduct a survey of quantity and arrangement of embryos in tropical eastern Pacific cupuladriid colonies and compare this to the frequency of cloning. Species populations show considerable variation in embryonic brooding. Patterns of brooding, both across and within species strongly support the hypothesis that as cloning increases, investment into sexual reproduction decreases. We find preliminary evidence that individual cupuladriid colonies that propagate sexually may senesce like solitary organisms, while species that regularly clone only appear to experience senescence at the level of the zooid.