Intrasexual competition and sexual selection in cooperative mammals

In most animals, the sex that invests least in its offspring competes more intensely for access to the opposite sex and shows greater development of secondary sexual characters than the sex that invests most. However, in some mammals where females are the primary care-givers, females compete more frequently or intensely with each other than males. A possible explanation is that, in these species, the resources necessary for successful female reproduction are heavily concentrated and intrasexual competition for breeding opportunities is more intense among females than among males. Intrasexual competition between females is likely to be particularly intense in cooperative breeders where a single female monopolizes reproduction in each group. Here, we use data from a twelve-year study of wild meerkats (Suricata suricatta), where females show high levels of reproductive skew, to show that females gain greater benefits from acquiring dominant status than males and traits that increase competitive ability exert a stronger influence on their breeding success. Females that acquire dominant status also develop a suite of morphological, physiological and behavioural characteristics that help them to control other group members. Our results show that sex differences in parental investment are not the only mechanism capable of generating sex differences in reproductive competition and emphasize the extent to which competition for breeding opportunities between females can affect the evolution of sex differences and the operation of sexual selection.     

Chromosomal effects of adeno-associated virus vector integration.

Adeno-associated virus (AAV) vectors are currently being used in several clinical gene-therapy trials (see the NIH OBA Human Gene Transfer Clinical Trials Database); however, little is known about the chromosomal effects of vector integration. Here we report that integrated vector proviruses are associated with chromosomal deletions and other rearrangements and are frequently located on chromosome 19 (although not at the wildtype AAV integration site).     

Myosin motor function: the ins and outs of actin-based membrane protrusions

Cells build plasma membrane protrusions supported by parallel bundles of F-actin to enable a wide variety of biological functions, ranging from motility to host defense. Filopodia, microvilli and stereocilia are three such protrusions that have been the focus of intense biological and biophysical investigation in recent years. While it is evident that actin dynamics play a significant role in the formation of these organelles, members of the myosin superfamily have also been implicated as key players in the maintenance of protrusion architecture and function. Based on a simple analysis of the physical forces that control protrusion formation and morphology, as well as our review of available data, we propose that myosins play two general roles within these structures: (1) as cargo transporters to move critical regulatory components toward distal tips and (2) as mediators of membrane-cytoskeleton adhesion.     

Outer hair cells in the mammalian cochlea and noise-induced hearing loss

Hair cells in the mammalian cochlea transduce mechanical stimuli into electrical signals leading to excitation of auditory nerve fibres. Because of their important role in hearing, these cells are a possible site for the loss of cochlear sensitivity that follows acoustic overstimulation. We have recorded from inner and outer hair cells (IHC, OHC) in the guinea pig cochlea during and after exposure to intense tones. Our results show functional changes in the hair cells that may explain the origin of noise-induced hearing loss. Both populations of hair cells show a reduction in amplitude and an increase in the symmetry of their acoustically evoked receptor potentials. In addition, the OHCs also suffer a sustained depolarization of the membrane potential. Significantly, the membrane and receptor potentials of the OHCs recover in parallel with cochlear sensitivity as measured by the IHC receptor potential amplitude and the auditory nerve threshold. Current theories of acoustic transduction suggest that the mechanical input to IHCs may be regulated by the OHCs. Consequently, the modified function of OHCs after acoustic overstimulation may determine the extent of the hearing loss following loud sound.     

Strategy

It may perhaps seem superfluous at the present time to emphasize the distinction between strategy and tactics. Moreover definitions are rarely quite satisfactory, for they can seldom be perfectly clear and at the same time perfectly comprehensive. Yet, since it is necessary that the parties to any discussion should have some common starting point, it will be as well to begin by stating exactly what is meant to be included. (The Encylcopaedia Britannica, 11th ed., Vol, 26, p. 347).     

Long-term increases in clutch size in common snapping turtles (Chelydra serpentina) and diamondback terrapins (Malaclemys terrapin)

Clutch size (CS) is a well-studied life history characteristic, and optimal egg size theory predicts that CS should correlate positively with reproductive investment. Turtles are good subjects for studies of reproductive strategies because few turtle species exhibit parental care; therefore quantifying their short-term reproductive investment is mostly limited to measuring egg size and number. Clutch size is usually reported as an average value for each turtle population, and where CS variation is noted, it is usually attributable to variation in adult body size. In two long-term studies of ecologically dissimilar species we detected a dramatic increase in CS in a common snapping turtle (Chelydra serpentina) population and in a diamondback terrapin (Malaclemys terrapin) population. It is unknown whether these changes are due to either variation in adult body size or resource availability; but the temporal patterns we observed have apparently never been reported previously. These trends remain unexplained and should be explored further.