Maturation shifts in a temperate marine fish population cannot be explained by simulated changes in temperature-dependent growth and maturity

To disentangle genetic and environmental influences on phenotypic traits that influence maturation of fish, it would be useful to predict the expected change due to environment alone to compare with observations. This requires a realistically scaled, species-specific life history model of environmentally determined variation in individual growth and maturation. In this study, inter-annual variability in the proportion of mature haddock in the west North Sea was predicted using a stochastic, individual-based simulation model incorporating a temperature-dependent maturation threshold. This species and region are particularly relevant to the debate about the relative importance of genetic and climate change because North Sea haddock have experienced both high fishing mortality and substantial warming in recent decades. Using observed temperatures in combination with temperature-dependent models for growth and maturation, the simulation model predicted year-to-year variation in length and maturity at age expected for cohorts produced from 1979 to 2006. The simulated proportions mature at age 2 were then compared to the observed proportions in an annual bottom trawl survey. Although the model explained much of the high-frequency variation in maturation, the simulated time trend under-represented the rate of increase in the observed trend in proportions mature. This inability of the temperature-dependent life history model to predict the magnitude of change appears consistent with a long-term decline in the maturation threshold. This result provides indirect support for a genetic change in a key life history trait.     

Dioxion-/Furan-’Verbrennungsprofile’ aus Hochtemperaturprozessen

Present knowledge assumes that different mechanisms acting downstream in high temperature processes lead to the formation of polychlorinated dibenzo(p)dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Concerning the 17 2,3,7,8-Cl-substituted PCDD/F congeners in particular, there is new evidence for a single-step reaction type (recently reported in this publication series, of. also parts 1 and 2). A formation based on a combination of the several mechanisms, which have been proposed and discussed since 1985, becomes more and more unlikely. Qualitatively the PCDD/F formation downstream from high temperature processes depends rather on a thermodynamically forced single reaction step, and on pure statistical distribution quantitatively. This may be a new ‘Thermostat Synthesis’ instead of ‘de novo’.     

“Chance” and mixed-species associations

Summary Spatial associations between members of different animal species may arise through mutual behavioral attraction, through attraction to common resources or locations, or by chance. I outline a means of calculating the expected duration of associations based on the null hypothesis that members of different species move independently and randomly. Observed association durations can be compared to these expectations to identify those cases of association (or avoidance) that have biologically interesting causes. The method is applicable to any species in which the presence of a second species can be recorded during focal samples of an individual or a cohesive social group. The data required are readily collected in the field; I illustrate the use of the technique with data from several East African forest primates.     

Persistence of rock-derived nutrients in the wet tropical forests of La Selva, Costa Rica

We used strontium isotopes and analysis of foliar and soil nutrients to test whether erosion can rejuvenate the supply of rock-derived nutrients in the lowland tropical rain forest of La Selva, Costa Rica. We expected that these nutrients would be depleted from soils on stable surfaces, a result of over one million years of weathering in situ. In fact, trees and palms in all landscape positions derive a relatively high percentage (> or =40%) of their strontium from bedrock, rather than atmospheric, sources. The fraction that is rock-derived increases on slopes, but with no detectable effect on plant macronutrient concentrations. These results differ from those in a similar ecosystem on Kauai, Hawaii, where plants on uneroded surfaces derive almost all of their foliar Sr from atmospheric, rather than bedrock, sources. The results from La Selva challenge the assumption that tropical Oxisols in general have low nutrient inputs from bedrock, and support the hypothesis that erosion can increase the supply of these nutrients in lower landscape positions.     

Fish distributions and nutrient cycling in streams: can fish create biogeochemical hotspots?

Rates of biogeochemical processes often vary widely in space and time, and characterizing this variation is critical for understanding ecosystem functioning. In streams, spatial hotspots of nutrient transformations are generally attributed to physical and microbial processes. Here we examine the potential for heterogeneous distributions of fish to generate hotspots of nutrient recycling. We measured nitrogen (N) and phosphorus (P) excretion rates of 47 species of fish in an N-limited Neotropical stream, and we combined these data with population densities in each of 49 stream channel units to estimate unit- and reach-scale nutrient recycling. Species varied widely in rates of N and P excretion as well as excreted N:P ratios (6-176 molar). At the reach scale, fish excretion could meet >75% of ecosystem demand for dissolved inorganic N and turn over the ambient NH4 pool in <0.3 km. Areal N excretion estimates varied 47-fold among channel units, suggesting that fish distributions could influence local N availability. P excretion rates varied 14-fold among units but were low relative to ambient concentrations. Spatial variation in aggregate nutrient excretion by fish reflected the effects of habitat characteristics (depth, water velocity) on community structure (body size, density, species composition), and the preference of large-bodied species for deep runs was particularly important. We conclude that the spatial distribution of fish could indeed create hotspots of nutrient recycling during the dry season in this species-rich tropical stream. The prevalence of patchy distributions of stream fish and invertebrates suggests that hotspots of consumer nutrient recycling may often occur in stream ecosystems.     

Maternal investment in rhesus macaques (Macaca mulatta): reproductive costs and consequences of raising sons

Maternal investment in offspring is expected to vary according to offspring sex when the reproductive success of the progeny is a function of differential levels of parental expenditure. We conducted a longitudinal investigation of rhesus macaques to determine whether variation in male progeny production, measured with both DNA fingerprinting and short tandem repeat marker typing, could be traced back to patterns of maternal investment. Males weigh significantly more than females at birth, despite an absence of sex differences in gestation length. Size dimorphism increases during infancy, with maternal rank associated with son’s, but not daughter’s, weight at the end of the period of maternal investment. Son’s, but not daughter’s, weight at 1 year of age is significantly correlated with adult weight, and male, but not female, weight accounts for a portion of the variance in reproductive success. Variance in annual offspring output was three- to fourfold higher in males than in females. We suggest that energetic costs of rearing sons could be buffered by fetal delivery of testosterone to the mother, which is aromatized to estrogen and fosters fat accumulation during gestation. We conclude that maternal investment is only slightly greater in sons than in daughters, with mothers endowing sons with extra resources because son, but not daughter, mass has ramifications for offspring sirehood. However, male reproductive tactics supersede maternal investment patterns as fundamental regulators of male fitness. Received: 23 July 1999 / Received in revised form: 23 February 2000 / Accepted: 13 March 2000