The Cost of Male Aggression and Polygyny in California Sea Lions (Zalophus californianus)

In polygynous mating systems, males often increase their fecundity via aggressive defense of mates and/or resources necessary for successful mating. Here we show that both male and female reproductive behavior during the breeding season (June–August) affect female fecundity, a vital rate that is an important determinant of population growth rate and viability. By using 4 years of data on behavior and demography of California sea lions (Zalophus californianus), we found that male behavior and spatial dynamics—aggression and territory size—are significantly related to female fecundity. Higher rates of male aggression and larger territory sizes were associated with lower estimates of female fecundity within the same year. Female aggression was significantly and positively related to fecundity both within the same year as the behavior was measured and in the following year. These results indicate that while male aggression and defense of territories may increase male fecundity, such interactions may cause a reduction in the overall population growth rate by lowering female fecundity. Females may attempt to offset male-related reductions in female fecundity by increasing their own aggression—perhaps to defend pups from incidental injury or mortality. Thus in polygynous mating systems, male aggression may increase male fitness at the cost of female fitness and overall population viability

Population resistance to climate change: modelling the effects of low recruitment in open populations

Isolated populations or those at the edge of their distribution are usually more sensitive to changes in the environment, such as climate change. For the barnacle Semibalanus balanoides (L.), one possible effect of climate change is that unpredictable spring weather could lead to the mismatching of larval release with spring phytoplankton bloom, hence reducing the recruitment. In this paper, model simulations of a variable open population with space limited recruitment were used to investigate the effects of low and zero recruitment on population abundance in S. balanoides. Data for model parameters was taken from an isolated population in the Isle of Man, British Isles. Model simulations with observed frequencies of years with low recruitment showed only small changes in population dynamics. Increased frequencies of low recruitment had large effects on the variation in population growth rate and free space and on population structure. Furthermore, populations with intermediate to high frequencies of low recruitment appeared more sensitive to additional changes in recruitment. Exchanging low recruitment with zero recruitment severely increased the risk of local extinctions. Simulations with consecutive years of low recruitment showed a substantial increase in free space and an increase in the time taken to recover to normal densities. In conclusion, model simulations indicate that variable populations can be well buffered to changes in the demography caused by introduced environmental noise, but also, that intermediate to high frequencies of disturbance can lead to a swift change in population dynamics, which in turn, may affect the dynamics of whole communities

Assessment of young and aged hematopoietic stem cell activity by competitive serial transplantation assays

Healthy hematopoietic stem cells (HSCs) are capable to self-renew and reconstitute the complete hematopoietic system. Upon aging, there is an increased incidence of blood-related diseases. Age-related phenotypes have been widely studied by bone marrow transplantation experiments, where reconstitution of the transplanted cells is a direct measure of HSC activity. In this protocol we describe a competitive bone marrow transplantation assay to functionally test young and old HSCs

TGF beta-induced switch from adipogenic to osteogenic differentiation of human mesenchymal stem cells: identification of drug targets for prevention of fat cell differentiation

Background: Patients suffering from osteoporosis show an increased number of adipocytes in their bone marrow, concomitant with a reduction in the pool of human mesenchymal stem cells (hMSCs) that are able to differentiate into osteoblasts, thus leading to suppressed osteogenesis.Methods: In order to be able to interfere with this process, we have investigated in-vitro culture conditions whereby adipogenic differentiation of hMSCs is impaired and osteogenic differentiation is promoted. By means of gene expression microarray analysis, we have investigated genes which are potential targets for prevention of fat cell differentiation.Results: Our data show that BMP2 promotes both adipogenic and osteogenic differentiation of hMSCs, while transforming growth factor beta (TGF beta) inhibits differentiation into both lineages. However, when cells are cultured under adipogenic differentiation conditions, which contain cAMP-enhancing agents such as IBMX of PGE2, TGF beta promotes osteogenic differentiation, while at the same time inhibiting adipogenic differentiation. Gene expression and immunoblot analysis indicated that IBMX-induced suppression of HDAC5 levels plays an important role in the inhibitory effect of TGF beta on osteogenic differentiation. By means of gene expression microarray analysis, we have investigated genes which are downregulated by TGF beta under adipogenic differentiation conditions and may therefore be potential targets for prevention of fat cell differentiation. We thus identified nine genes for which FDA-approved drugs are available. Our results show that drugs directed against the nuclear hormone receptor PPARG, the metalloproteinase ADAMTS5, and the aldo-keto reductase AKR1B10 inhibit adipogenic differentiation in a dose-dependent manner, although in contrast to TGF beta they do not appear to promote osteogenic differentiation.Conclusions: The approach chosen in this study has resulted in the identification of new targets for inhibition of fat cell differentiation, which may not only be relevant for prevention of osteoporosis, but also of obesity

Impacts of global changes and extreme hydroclimatic events on macroinvertebrate community structures in the French Rhône River

We assessed the temporal changes in and the relationships between the structures of the macroinvertebrate communities and the environmental conditions of the French Rhône River (the river from Lake Geneva to the Mediterranean Sea) over the last 20 years (1985–2004). Multisite environmental and biological datasets were analysed using multiple CO-inertia analysis (MCOA) and Procrustean analysis. Changes in environmental conditions were mainly marked by an improvement in water quality between 1985 and 1991 and by an increase in water temperature from 1985 onwards due to climate change. Improvement in water quality seemed to delay changes in community structures under global warming. We then observed trends in community structures coupled with high temperatures and a decrease in oxygen content. Interestingly, we observed both gradual changes and rapid switches in community states. These shifts seemed coupled to extreme hydroclimatic events (i.e. pulse disturbances). Floods and the 2003 heatwave enhanced the development of eurytolerant and invasive taxa which were probably able to take advantage of gradual warming environmental conditions. Despite various site-specific “press” constraints (e.g. hydropower schemes, nuclear power plants), similar changes in community structures were observed along the French Rhône River. Such consistency in temporal processes at large geographical scales underlined the strength of hydroclimatic constraints on community dynamics compared to specific local disturbances. Finally, community structures did not show any sign of recovery, and their relative sensitivities to extreme hydroclimatic events seemed to increase with time. Thus, our results suggest that global changes may reduce the resilience of current community states