Geographical variation in offspring size effects across generations

Offspring size is thought to strongly affect offspring fitness and many studies have shown strong offspring size/fitness relationships in marine and terrestrial organisms. This relationship is strongly mitigated by local environmental conditions and the optimal offspring size that mothers should produce will vary among different environments. It is assumed that offspring size will consistently affect the same traits among populations but this assumption has not been tested. Here I use a common garden experiment to examine the effects of offspring size on subsequent performance for the marine bryozoan Bugula neritina using larvae from two very different populations. The local conditions at one population (Williamstown) favour early reproduction whereas the other population (Pt. Wilson) favours early growth. Despite being placed in the same habitat, the effects of parental larval size were extremely variable and crossed generations. For larvae from Williamstown, parental larval size positively affected initial colony growth and larval size in the next generation. For larvae from the other population, parental larval size positively affected colony fecundity and negatively affected larval size in the next generation. Traditionally, exogenous factors have been viewed as the sole source of variation in offspring size/fitness relationship but these results show that endogenous factors (maternal source population) can also cause variation in this crucial relationship. It appears offspring size effects can be highly variable among populations and organisms can adapt to local conditions without changing the size of their offspring.     

Temperature preference and reproductive fitness of the annual killifish Austrofundulus limnaeus exposed to constant and fluctuating temperatures

Austrofundulus limnaeus thrive in ephemeral ponds that may experience temperatures spanning a range of over 20°C on a daily basis. We hypothesized that A. limnaeus may have mechanisms, either behavioral or physiological, that allow them to support successful reproduction in this environment. To evaluate this hypothesis, we exposed male and female adult A. limnaeus to constant 26°C and cycling 21–37°C acclimation regimes in the laboratory and then determined their temperature preference and reproductive fitness. Temperature preference was determined using a thermal gradient. We demonstrated that A. limnaeus is capable of accurate behavioral thermoregulation, has a final thermal preferendum near 26°C, and exhibits a daily cycle of temperature preference. Exposure to a cycling temperature regime has an acute effect on thermal preference that differs between the sexes. Reproductive capability was negatively affected by the cyclic temperature exposure. These findings suggest that thermal partitioning between males and females may be a natural part of the ecology of A. limnaeus. In addition, it appears that behavioral thermoregulation, or partitioning of reproductive events to the cool parts of the thermoperiod, are likely to be critical to support successful reproduction in natural populations of A. limnaeus.     

Are MUPs a Toxic Waste Disposal System?

Male house mice produce large quantities of major urinary proteins (MUPs), which function to bind and transport volatile pheromones, though they may also function as scavengers that bind and excrete toxic compounds (‘toxic waste hypothesis’). In this study, we demonstrate the presence of an industrial chemical, 2,4-di-tert-butylphenol (DTBP), in the urine of wild-derived house mice (Mus musculus musculus). Addition of guanidine hydrochloride to male and female urine resulted in an increased release of DTBP. This increase was only observed in the high molecular weight fractions (HMWF; > 3 kDa) separated from male or female urine, suggesting that the increased release of DTBP was likely due to the denaturation of MUPs and the subsequent release of MUP-bound DTBP. Furthermore, when DTBP was added to a HMWF isolated from male urine, an increase in 2-sec-butyl-4,5-dihydrothiazole (SBT), the major ligand of MUPs and a male-specific pheromone, was observed, indicating that DTBP was bound to MUPs and displaced SBT. These results suggest that DTBP is a MUP ligand. Moreover, we found evidence for competitive ligand binding between DTBP and SBT, suggesting that males potentially face a tradeoff between eliminating toxic wastes versus transporting pheromones. Our findings support the hypothesis that MUPs bind and eliminate toxic wastes, which may provide the most important fitness benefits of excreting large quantities of these proteins.     

Nanoscale increases in CD2-CD48-mediated intermembrane spacing decrease adhesion and reorganize the immunological synapse

The relationship between intermembrane spacing, adhesion efficiency, and lateral organization of adhesion receptors has not been established for any adhesion system. We have utilized the CD2 ligand CD48 with two (wild type CD48 (CD48-WT)), four (CD48-CD2), or five (CD48-CD22) Ig-like domains. CD48-WT was 10-fold more efficient in mediating adhesion than CD48-CD2 or CD48-CD22. Electron tomography of contact areas with planar bilayers demonstrated average intermembrane spacing of 12.8 nm with CD48-WT, 14.7 nm with CD48-CD2, and 15.6 nm with CD48-CD22. Both CD48-CD2 and CD48-CD22 chimeras segregated completely from CD48-WT in mixed contact areas. In contrast, CD48-CD2 and CD48-CD22 co-localized when mixed contacts were formed. Confocal imaging of immunological synapses formed between primary T lymphocytes and Chinese hamster ovary cells presenting major histocompatibility complex-peptide complexes, and different forms of CD48 demonstrated that CD48-CD2 and CD48-CD22 induce an eccentric CD2/T cell antigen receptor cluster. We propose that this reorganization of the immunological synapse sequesters the T cell antigen receptor in a location where it cannot interact with its ligand and dramatically reduces T cell sensitivity.     

Interactions between CdsD, CdsQ, and CdsL, three putative Chlamydophila pneumoniae type III secretion proteins

Chlamydophila pneumoniae is a gram-negative obligate intracellular bacterial pathogen that causes pneumonia and bronchitis and may contribute to atherosclerosis. The developmental cycle of C. pneumoniae includes a morphological transition from an infectious extracellular elementary body (EB) to a noninfectious intracellular reticulate body (RB) that divides by binary fission. The C. pneumoniae genome encodes a type III secretion (T3S) apparatus that may be used to infect eukaryotic cells and to evade the host immune response. In the present study, Cpn0712 (CdsD), Cpn0704 (CdsQ), and Cpn0826 (CdsL), three C. pneumoniae genes encoding yersiniae T3S YscD, YscQ, and YscL homologs, respectively, were cloned and expressed as histidine- and glutathione S-transferase (GST)-tagged proteins in Escherichia coli. Purified recombinant proteins were used to raise hyper-immune polyclonal antiserum and were used in GST pull-down and copurification assays to identify protein-protein interactions. CdsD was detected in both EB and RB lysates by Western blot analyses, and immunofluorescent staining demonstrated the presence of CdsD within inclusions. Triton X-114 solubilization and phase separation of chlamydial EB proteins indicated that CdsD partitions with cytoplasmic proteins, suggesting it is not an integral membrane protein. GST pull-down assays indicated that recombinant CdsD interacts with CdsQ and CdsL, and copurification assays with chlamydial lysates confirmed that native CdsD interacts with CdsQ and CdsL. To the best of our knowledge, this is the first report demonstrating interactions between YscD, YscQ, and YscL homologs of bacterial T3S systems. These novel protein interactions may play important roles in the assembly or function of the chlamydial T3S apparatus.     

Offspring size plasticity in response to intraspecific competition: an adaptive maternal effect across life-history stages

When provisioning offspring, mothers balance the benefits of producing a few large, fitter offspring with the costs of decreased fecundity. The optimal balance between offspring size and fecundity depends on the environment. Theory predicts that larger offspring have advantages in adverse conditions, but in favorable conditions size is less important. Thus, if environmental quality varies, selection should favor mothers that adaptively allocate resources in response to local conditions to maximize maternal fitness. In the bryozoan Bugula neritina, we show that the intensity of intraspecific competition dramatically changes the offspring size/performance relationship in the field. In benign or extremely competitive environments, offspring size is less important, but at intermediate levels of competition, colonies from larger larvae have higher performance than colonies from smaller larvae. We predicted mothers should produce larger offspring when intermediate competition is likely and tested these expectations in the field by manipulating the density of brood colonies. Our findings matched expectations: mothers produced larger larvae at high densities and smaller larvae at low densities. In addition, mothers from high-density environments produced larvae that have higher dispersal potential, which may enable offspring to escape crowded environments. It appears mothers can adaptively adjust offspring size to maximize maternal fitness, altering the offspring phenotype across multiple life-history stages.