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Knowledge of prey sizes consumed by a predator aids in the estimation of predation impact. Young-of-the year bluefish, Pomatomus saltatrix, attack their prey tail-first and often bite their prey in half; this poses a unique problem in determining prey sizes from stomach content analysis. We developed a series of linear regressions to estimateoriginal prey lengths from measurements of eye diameter and caudal peduncle depth for striped bass, Morone saxatilis, bay anchovy, Anchoamitchilli, American shad, Alosa sapidissima, blueback herring, Alosaaestivalis, Atlantic silverside, Menidia menidia, and white perch, Morone americana. We then used these regressions to estimate original prey sizes from pieces of prey found in stomachs of bluefish collect ed in the Hudson River estuary from 1990--1993. Lengths of prey that were swallowed whole were compared to estimated lengths of prey that were consumed in pieces. Lengths of prey that were consumed in pieceswere larger than prey that were consumed whole. We determined the prey length/predator length ratio at which bluefish began shifting fromswallowing their prey whole to partial consumption. Shifting occurred at a ratio of approximately 0.35 irrespective of prey species, suggesting that prey length plays an important role in predator foraging decisions and may contribute to gape limitations. Shifts in foraging mode effectively reduce gape limitation and allow bluefish to consumelarger prey sizes which may increase their effect on prey populations. [ABSTRACT FROM AUTHOR]

Latitudinal populations of the Atlantic silverside, Menidia menidia, show substantial genetic variation in rates of energy acquistion and allocation. Reared in common environments, silversides from northern latitudes consume more food, grow faster and more efficiently, store more energy, and produce greater quantities of eggs than their southern conspecifics. The persistence of seemingly inferior southern genotypes in the face of ostensibly superior northern genotypes suggest that there are hidden evolutionary trade-offs associated with these elevated acquisition and allocation rates. We tested the hypothesis that rapid growth and high levels of food consumption trade-off against locomotory performance in M. menidia. We compared both aerobic (prolonged and endurance) and anaerobic (burst) swimming capacities between intrinsically fast-growing fish from the north (Nova Scotia, NS) and intrinsically slow-growing fish from the south (South Carolina, SC) and between growth-manipulated phenotypes within each population. We also compared swimming speeds and endurance between fasted and recently fed fish within populations. Maximum prolonged and burst swimming speeds of NS fish were significantly lower than those of SC fish, and swimming speeds of fast-growing phenotypes were lower than those of slow-growing phenotypes within populations. Fed fish had lower burst speeds and less endurance than fasted fish from the same population. Thus, high rates of growth and the consumption of large meals clearly diminish swimming performance, which likely increases vulnerability to predation and decreases survival and relative fitness. The submaximal growth rate of southern M. menidia appears to be adaptive, resulting from balancing selection on rates of somatic growth.

We identified five human T-lymphoid cell lines (PB-1, Sez-4, C19PL, HUT 102B and ATL-2) which highly express CD4 in addition to CXCR4 and CCR5. In order to evaluate if these cells are infectabile by human immunodeficiency virus (HIV) and could be employed as a model in HIV research we exposed these cell lines to X4 (T-cell tropic) and R5 (macrophage tropic) and subsequently tried to correlate their infectability with (i) level of chemokine coreceptor (CXCR4 and CCR5) expression, (ii) coreceptor functionality (calcium flux, chemotaxis and phosphorylation of MAPK p42/44 and AKT) and (iii) endogenous expression and secretion of HIV-related chemokines which compete with the virus for binding to CXCR4 (SDF-1/CXCL12) or CCR5 (MIP-1beta/CCL4, MIP-1alpha/CCL3, RANTES/CCL5, MCP-2/CCL8, MCP-3/CCL7 and MCP-4/CCL13). We demonstrated that while PB-1 cells are infectable by both X4 and R5 HIV, Sez-4, C91PL, HUT 102B and ATL-2 cells were infected by X4 HIV only. Moreover, we noticed that the susceptibility of these cells to HIV did not correspond either with the level of surface expression or with the functionality of CXCR4 or CCR5; however, it was modulated to some degree by the endogenously secreted HIV-related chemokines. Thus all five mature T-cell lines described here may provide useful new models for studying various aspects of HIV infection. In addition we demonstrate that the infectability of cells by HIV is modulated by so far unidentified intrinsic factors as well as some already known endogenously secreted chemokines. The identification of these factors may be important for developing new strategies to protect cells from HIV infection.

The Atlantic silverside (Menidia menidia) exhibits countergradient latitudinal variation in somatic growth rate along the East Coast of North America. Larvae and juveniles from high-latitude populations display higher intrinsic rates of energy consumption and growth than genotypes from low-latitude populations. The existence of submaximal growth in some environments suggests that trade-offs must counter the oft-cited theoretical benefits of energy and growth maximization (e.g., "bigger is better,'' ''faster is better'') in the immature life stages. We hypothesized that energy and growth maximization trades off against investment in defense from predators. We conducted laboratory selection experiments to compare vulnerability to predation of silversides from: (1) fast-growing northern (Nova Scotia, NS) versus slow-growing southern (South Carolina, SC) source populations; (2) phenotypically manipulated fast-growing versus moderately-growing NS fish; and (3) recently fed versus unfed NS and SC fish. Tests involved fish drawn from common-garden environments and were conducted by subjecting mixed-treatment schools of size-matched silversides to natural, common piscine predators. NS silversides suffered significantly higher predation mortality than SC silversides. Parallel results were found in phenotypic manipulation of growth: NS silversides reared on a fast-growth trajectory (approximately 1.0 mm/day) were significantly more vulnerable to predation than those growing at a moderate rate (approximately 0.5 mm/day). Food consumption also affected vulnerability to predators: Silversides with large meals in their stomachs suffered significantly higher predation mortality than unfed silversides. Differences in predation vulnerability were likely due to swimming performance, not attractiveness to predators. Our findings demonstrate that maximization of energy intake and growth rate engenders fitness costs in the form of increased vulnerability to predation.

Countergradient variation is a geographical pattern of genotypes (with respect to environments) in which genetic influences on a trait oppose environmental influences, thereby minimizing phenotypic change along the gradient. Phenotypic similarity across changing environments ought to be of intense interest because it belies considerable genotypic change. When it occurs in characters that are positively associated with fitness, countergradient variation conflicts with the hypothesis that local adaptation to one environment trades off against performance in another environment. Cases of countergradient variation therefore offer unique insight into the mechanisms that produce and maintain phenotypic similarity and/or differences along environmental gradients., (Copyright © 1995. Published by Elsevier Ltd.)

Balanced (1 to 1) sex ratios are thought to evolve by a process known as frequency- dependent selection of the minority sex. Five populations of a fish with genetically based variation in temperature-dependent sex determination were maintained for 5 to 6 years in artificial constant-temperature environments that initially caused the sex ratio to be highly skewed. Increases in the proportion of the minority sex occurred in subsequent generations until a balanced sex ratio was established, thus confirming a central premise underlying the theory of sex-ratio evolution.

Two general mechanisms of sex determination have been identified among gonochoristic vertebrates: environmental sex determination where offspring become male or female in response to an environmental factor(s) during development (for example, some fishes and reptiles); and genetic sex determination where sex is determined by genotype at conception (as in birds and mammals). How do these sex-determining systems evolve? Direct evidence is virtually non-existent because the sex-determining systems of most species appear to have little genetic variation. Here we provide the first evidence of adaptive variation in environmental and genetic sex determination within a species. We show that in a fish with temperature-dependent sex determination, populations at different latitudes compensate for differences in thermal environment and seasonality by adjusting the response of sex ratio to temperature, and by altering the level of environmental as opposed to genetic control. The adjustments observed are precisely those predicted by adaptive sex ratio theory.

Sex determination in an atherinid fish, the Atlantic silverside (Menidia menidia), is under the control of both genotype and temperature during a specific period of larval development. The sex ratios of the progeny of different females are variable and differ in their responsiveness to temperature. This demonstrates that sex ratio in fishes that normally have separate sexes can be influenced by the environment.