Self-monitoring of reproductive success: nest switching in the redlip blenny (Pisces: Blenniidae)

Summary In the redlip blenny Ophioblennius atlanticus, commonly found on Caribbean reefs, eggs are laid in a male's nest and are guarded by the male until they hatch as planktonic larvae. Male reproductive success, defined as the number of egg batches hatched per reproductive period, was positively correlated with male size and with the inner surface area of the male's nest. Male blennies often switch nests between reproductive periods. Most nest switching (83%) occurred following periods of low reproductive success. Moreover, a male having low reproductive success was more likely to switch if the inner surface area of his nest was small. Most nest switching (72–80%) was to a nest of larger surface area than the previous nest. In 72% of all switches, males had higher reproductive success in the period following the switch than in the one preceding it. The results suggest that male redlip blennies monitor their current reproductive success and the characteristics of their current nests, switch to better nests if their reproductive success is low, and typically benefit from the decision to do so. These capabilities have seldom been demonstrated in any phylum.     

Feeding habits of marine cladocerans in the Inland Sea of Japan

Natural food items of five species of marine cladocerans, Evadne nordmanni, E. tergestina, Penilia avirostris, Podon leuckarti and P. polyphemoides, were investigated in the Inland Sea of Japan between April 1986 and May 1987. Gut content examination with SEM (scanning electron microscopy) revealed that feeding was largely limited to centric diatoms and a few exceptions of pennate diatoms and dinoflagellates. No animal remains were detected, and some unidentified materials were also found. Phytoplankton smaller than 35 m in size (cell diameter in centric diatoms and longest dimension in others) was found most frequently in the gut of cladocerans. The role of grazing of marine cladocerans in trophodynamic pathways of the pelagic realm is discussed.     

Pathways of arsenic uptake and incorporation in estuarine phytoplankton and the filter-feeding invertebrates Eurytemora affinis,Balanus improvisus and Crassostrea virginica

Arsenic uptake from water and from phytoplankton was followed in the copepod Eurytemora affinis and the barnacle Balanus improvisus collected from the Patuxent River estuary, Chesapeake Bay, eastern coast of the USA in 1987, and in the oyster Crassostrea virginica obtained from a hatchery on the shore of Chesapeake Bay in 1987. Dissolved arsenic was readily taken up by phytoplankton and by shell material of B. improvisus and C. virginica; however, no dissolved arsenic was incorporated into the invertebrate tissues. When E. affinis, B. improvisus and C. virginica were fed phytoplankton containing elevated arsenic contents, significant arsenic incorporation occurred. Juvenile B. improvisus incorporated relatively more arsenic than adults of all three species. Compared to the 100 to 200% increase in arsenic content by phytoplankton exposed to dissolved arsenic, the 25 to 50% increase in these invertebrate species via trophic transfer is relatively small. Even though the trophic pathway for arsenic transfer is the major one for higher trophic levels within an ecosystem, the potential for direct arsenic impact to trophic levels other than phytoplankton appears to be minimal.     

Dispersion of displaying male sage grouse

Summary The degree to which male sage grouse select lek sites and females select nesting sites to maximize proximity to the other sex was examined by contrasting male dispersions with the dispersions and movements of females in the months preceeding incubation. Wintering females exhibit highly overlapping ranges due to shared use of central refuging areas. In late winter and early spring, females move an average 9 km from wintering areas to select nest sites and males begin occupying leks. Pooled evidence suggests that females select nest sites independently of male dispersion whereas males adjust lek occupation so as to maximize proximity to females. Relevant observations include females visiting nest sites before leks, moving further to select a nest site than to select a lek, and increasing their distance to leks as a result of selecting nest sites. In addition, males avoid leks until females have moved to within 5 km of the arenas, abandon early season leks as local female densities drop, and exhibit dispersions in which mean ratios of females/male are similar across leks. Contrasts between predicted and observed dispersions of males showed that hotspot settlement models are adequate to explain male dispersions on very coarse scales (2 km or greater); on finer scales, habitat preferences of males and tendencies for males to cluster tightly must be invoked in addition to hotspots to explain specific lek sitings.     

Genetically Effective Population Size of Large Mammals: An Assessment of Estimators

Calculamos tamuños de poblaciones genéticamente efectivas (N_e) para poblaciones simuladas del oso gris (Ursus arctos) trazando la péridida de heterozigasidad a tráves del tiempo, luego las comparamos con estimaciones de N_e Producidas aplicando fórmulas publicadas a los resultados demográficos de la simulación. Los valores de N_e calculados usando diferentes fórmula.s con datos idénticos, variaron mucho. Las ecuaciones publicadas por Hill (1972), y modificaciones de las usuadas por Ryman, et aL (1981) y Reed et al. (1986), proporcionaron los cálculos más precsios Fluctuaciones menores en las poblacionales tuvieron poco efecto sobre N_e pero la variación en el éxito repductivo por vida entre los machos V_km redujo tremendamente el N_e comparado con el valor esperado bajo exito reproductivo al azar. Todos los métodos para calcular N_e para poblaciones con demografias complejas requieren datos extensos, pero estimaciones para V_km en especies poligamas son especialmente dificiles de obtener. Sugerimos que modelos de simulación pueden proveer métodos alternutivos para calcular V_km y N_e.     

Mating system of the hermaphroditic coral-reef fish,Serranus baldwini

Summary The lantern bass, Serranus baldwini, is a small hermaphroditic serranid found adjacent to coral reefs throughout the Caribbean. Data from gonad inspection, spawning behavior, and gamete release from individuals all confirm that populations consist of simultaneous hermaphrodites and males. This gender pattern appears to be sequential, with larger males derived from smaller hermaphrodites. The social system is haremic, with the male defending an area containing 1–7 hermaphrodites. The social system and gender pattern are similar to those of the eastern Pacific serranid, Serranus fasciatus. Males obtain disproportionately high mating success by being nearly the sole mates of hermaphrodites within their harems. Hermaphrodites obtain very low levels of mating success through male function. This pattern may result from female choice by hermaphrodites, mate sequestering tactics by males, or both. The serranids that change gender from hermaphrodite to male appear to have a higher environmental potential for polygyny than other simultaneous hermaphrodites in this family. Factors that may maintain male function in hermaphroditic S. baldwini are outlined, but none currently provides clear evidence for why this species has not evolved to protogyny.     

Metabolic disposition of lactate in the horseshoe crab Limulus polyphemus and the stone crab Menippe mercenaria

The metabolism of ¹⁴C-labelled lactate was investigated in the horseshoe crab Limulus polyphemus and the stone crab Menippe mercenaria. When a bolus of (¹⁴C-U)-D-lactate was injected into L. polyphemus, there was substantial release pf ¹⁴CO₂ into the medium. In the case of M. mercenaria, ¹⁴CO₂ release was also observed after injection of (¹⁴C-U)-L-lactate into experimental individuals. Analysis of the distribution of radioactivity in whole body extracts of both species revealed easily detectable amounts of radioactivity in the glycogen fraction, although the bulk of the radioactivity was in the cation, anion/neutral and CO₂ fractions. To investigate the metabolism of lactate further, ¹⁴C-labelled lactate was injected into large individuals of L. polyphemus and M. mercenaria, and the distribution of radioactivity was determined in the hemolymph, muscle and hepatopancreas. Utilization of (¹⁴C-U)-D-lactate by L. polyphemus resulted in the accumulation of significant amounts of labelled glucose in all three body compartments as well as the production of labelled glycogen in the telson levator muscle and hepatopancreas. Utilization of (¹⁴C-U)-L-lactate resulted in a similar pattern of glucose and glycogen labelling in the hemolymph, cheliped muscle and hepatopancreas of M. mercenaria. These studies demonstrate that both L. polyphemus and M. mercenaria have the capacity for glyco- and gluconeogenesis using lactate as the substrate.