Seed development in Pisum

The Ih and lh _i alleles have been shown previously to reduce the level of endogenous gibberellin A₁ (GA₁) in shoots of pea (Pisum sativum L.), resulting in a dwarf phenotype compared with the wild type, cv. Torsdag (Lh). In addition, plants homozygous for the lh ⁱ allele have reduced seed yield compared with Lh (tall, wild type) and lh (dwarf) plants. In this paper we show that the lh ⁱ mutation is expressed in developing seeds and pods. Comparison of GA levels in young shoots and developing seeds of genotypes lh and lh ⁱ demonstrates that the relative severity of the two mutations varies in different tissues. Homozygous h ⁱ seeds have reduced GA levels, weigh less, and are less likely to develop to maturity when compared with Lh seeds. However, fertilization of lh ⁱ plants with Lh pollen increases seed GA levels, seed weight and seed survival, indicating that an increase in seed GA levels due to the presence of the Lh allele can restore normal seed growth. Pods developing on self-pollinated lh ⁱ plants are shorter than pods on Lh (wild type) plants, although this may be an indirect effect of the increased seed abortion of lh _i plants. Based on these results we suggest that endogenous GAs play an important role in the development of seeds of P. sativum L.Abbreviations GA_(n) gibberellin A_n We wish to thank Katherine McPherson, Peter Newman, Leigh Johnson and Peter Bobbi for technical assistance, Professor L. Mander (ANU, Canberra) and Professor B.O. Phinney (UCLA, USA) for labelled GA standards, and the Australian Research Council for financial support.     

Site fidelity in predictable and unpredictable habitats

Summary Site fidelity, the tendency to return to a previously occupied location, has been observed in numerous species belonging to at least three phyla. In this paper I develop a general model using dynamic programming to investigate conditions under which fidelity to a previously occupied territory will be advantageous. The results predict that site fidelity should be inversely related to heterogeneity in territory quality and the animal's lifespan and positively related to the cost of changing territories, age and probability of mortality in the habitat. The predictability of reproductive outcome (defined as the probability that next period's outcome will be the same as this period's outcome) also affects site fidelity. In predictable habitats, changing territories may be favoured after a bad previous outcome. In contrast, settlement should be independent of the previous outcome in unpredictable habitats. Individuals should also be site-faithful in unpredictable habitats, as long as the mean territory quality is equal among available territories. I also investigate the success of two potential decision rules (always stay and win-stay: lose-switch) relative to the optimal settlement strategy. The results show that these rules may perform as well as the optimal strategy under certain conditions. The always stay strategy does well in unpredictable habitats, when the mean quality within a territory is equal among territories. In contrast, the win-stay: lose-switch strategy performs best in predictable habitats.     

Patterns of fluctuating asymmetry in sexual ornaments predict female choice

Extravagant secondary sexual characters are assumed to have arisen and be maintained by sexual selection. While traits like horns, antlers and spurs can be ascribed to intrasexual competition, other traits such as extravagant feather ornaments, displays and pheromones have to be ascribed to mate choice. A number of studies have tested whether females exert selection on the size of male ornaments, but only some of these have recorded female preferences for the most extravagantly ornamented males. Here I demonstrate that female choice can be directly predicted from the relationship between the degree of fluctuating asymmetry and the size of a secondary sexual character. Fluctuating asymmetry is an epigenetic measure of the ability of individuals to cope with stress, and it occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. There is a negative relationship between the degree of fluctuating asymmetry and the absolute size of an ornament in those bird species with a female preference for the largest male sex trait, while there is a flat or U-shaped relationship among species without a female preference. These results suggest that females prefer exaggerated secondary sexual characters if they reliably demonstrate the ability of males to cope with genetic and environmental stress. Some species may demonstrate a flat or U-shaped relationship between the degree of fluctuating asymmetry and the absolute size of an ornament because (i) the genetic variance in viability signalled by the secondary sex trait has been depleted; (ii) the secondary sex trait is not particularly costly and therefore does not demonstrate condition dependence; or because (iii) the sex traits can be considered arbitrary traits rather than characters reflecting good genes.     

Extra-pair paternity and sexual dimorphism in birds

Differences in the strength of sexual selection between males and females can lead to sexual dimorphism. Extra-pair paternity (EPP) can increase the variance in male reproductive success and hence the opportunity for sexual selection. Previous research on birds suggests that EPP drives the evolution of dimorphism in plumage colour and in body size. Because EPP increases the intensity of sexual selection in males, it should lead to increased dimorphism in species with larger or more colourful males, but decreased dimorphism in species with larger or more colourful females. We explored the covariation between EPP and sexual dimorphism in wing length and plumage colouration in 401 bird species, while controlling for other, potentially confounding variables. Wing length dimorphism was associated positively with the frequency of EPP, but also with social polygamy, sex bias in parental behaviour and body size and negatively with migration distance. The frequency of EPP was the only predictor of plumage colour dimorphism. In support of our prediction, high EPP levels were associated with sexual dichromatism, positively in species in which males are more colourful and negatively in those in which females are more colourful. Contrary to our prediction, high EPP rates were associated with increased wing length dimorphism in species with both male- and female-biased dimorphism. The results support a role for EPP in the evolution of both size and plumage colour dimorphism. The two forms of dimorphism were weakly correlated and predicted by different reproductive, social and life-history traits, suggesting an independent evolution.     

Female reproductive fluid concentrations affect sperm performance of alternative male phenotypes in an external fertilizer

There is growing evidence that the female reproductive fluid (FRF) plays an important role in cryptic female choice through its differential effect on the performance of sperm from different males. In a natural spawning event, the male(s) may release ejaculate closer or further away from the spawning female. If the relative spatial proximity of competing males reflects the female pre-mating preference towards those males, then favoured males will encounter higher concentrations of FRF than unpreferred males. Despite this being a common situation in many external fertilizers, whether different concentrations of FRF can differentially influence the sperm performance of distinct male phenotypes (favoured and unfavoured by the female) remains to be elucidated. Here, we tested this hypothesis using the grass goby (Zosterisessor ophiocephalus), a fish with distinct territorial-sneaker reproductive tactics and female pre-mating preference towards territorial males, that consequently mate in an advantaged position and whose sperm experience higher concentrations of FRF. Our findings revealed a differential concentration-dependent effect of FRF over sneaker and territorial sperm motility only at low concentrations (i.e. at the distance where sneakers typically ejaculate), with increasing FRF concentrations (i.e. close to the eggs) similarly boosting the sperm performance of both sneaker and territorial males. The ability to release sperm close to the eggs is a prerogative of territorials, but FRF can likewise advantage the sperm of those sneakers that are able to get closer, allowing flexibility in the direction of female post-mating choice.     

The evolution of sexually dimorphic earwig forceps: social interactions among adults of the toothed earwig, Vostox apicedentatus

Earwigs (Insecta, Dermaptera) are characterized by uniquelyelaborated cerci, commonly called forceps, the function of whichremains unclear. We studied intrasexual and intersexual interactionsin the laboratory to examine the context and pattern of forcepsuse in the toothed earwig. Vostox apictdenlatus (Caudell). Interactionsbetween pairs of earwigs were recorded in four social situations:(1) two males, (2) two males plus a virgin female, (3) two females,and (4) one male and one female. Forceps were used as both weaponsand display structures by males and females in all of thesesocial contexts. During pairwise male-male interactions, onemale clearly dominated the other male. Dominant males were moreactive and more likely to use their forceps in intrasexual interactionsthan were subordinate males. In interactions where there weretwo males and one female present, the male that dominated male-maleinteractions was able to maintain exclusive access to the female.There was no indication of active female choice during or aftercourtship. During intersexual interactions, only males usedtheir forceps during courtship. The behavioral repertoire involvingforceps was greater for males than for females, especially inintrasexual contests. There was no clear outcome of intrasexualinteractions among females. These results suggest that forcepsfunction mainly as weapons in male-male interactions and mayhave evolved, at least in part, as a result of sexual selection.Further research is required to test for female mate choiceand to separate the various mechanisms of sexual selection ifmate choice exists. Comparative studies are needed to determineif sexual selection was the original evolutionary mechanismleading to the development of these unusual structures or ifsexual selection is relegated to a secondary effect, leadingto the elaboration and sexualdimorphism of these structuresin selected groups of earwigs.     

The direction of mothers' and daughters' preferences and the heritability of male ornaments in red jungle fowl (Gallus gallus)

We used a breeding design involving 18 sires and 108 dams tostudy the heritabilities of male ornaments in red jungle fowl(Gallus gallus). Ornaments used by females to choose mates showedlow heritabilities, with the exception of comb and wattle measures.The general absence of heritability suggests that a geneticcovariance did not exist at the time of this study between mostmale ornaments and female preferences for those ornaments. Thisresult is contrary to a key prediction of the arbitrary or Fisherianhypothesis of sexual selection. Comb size and color are condition-dependenttraits that reflect short-term changes in health, and comb sizeof males was positively correlated with offspring weight. Ourresults are consistent with the expectation of good-genes hypothesesthat male ornaments reflect the ability of males to withstandenvironmental stresses.     

Drug resistance in rat colon cancer cell lines is associated with minor changes in susceptibility to cytotoxic cells

The development of resistance to anticancer drugs urges the search for different treatment modalities. Several investigators have reported the concomitant development of drug resistance and resistance to natural killer (NK), lymphokine-activated killer (LAK) or monocyte/macrophage cell lysis, while others described unchanged or even increased susceptibility. We investigated this subject in the rat colon carcinoma cell line, CC531-PAR, which is intrinsically multidrug-resistant (MDR), and in three sublines derived from this parental cell line: a cell line with an increased MDR phenotype (CC531-COL), a revertant line from CC531-COL (CC531-REV), which demonstrates enhanced sensitivity to anticancer drugs of the MDR phenotype, and an independently developed cisplatin-resistant line (CC531-CIS). In a 4-h⁵¹Cr-release assay we found no difference in susceptibility to NK cell lysis. No significant differences in lysability by adherent LAK (aLAK) cells were observed in a 4-h assay. In a prolonged 20-h⁵¹Cr-release assay an enhanced sensitivity to aLAK-cell-mediated lysis was observed in the revertant, P-glycoprotein-negative cell line and in the cisplatin-resistant cell line (CC531-CIS). None of the cell lines was completely resistant to lysis by aLAK cells. Therefore, a role for immunotherapy in the treatment of drug-resistant tumors remains a realistic option.     

Influence of a Small Number of Mature T Cells in Donor Bone Marrow Inocula on Reconstitution of Lymphoid Tissues and Negative Selection of a T Cell Repertoire in the Recipient

Allo-chimerism and clonal elimination of self antigen (Ag) (Ia + Mls-1^a) reactive Vβ6+ T cells were analyzed and compared between allogeneic bone marrow (BM) chimeras reconstituted with BM cells which had been treated with anti-Thy-1 monoclonal antibody (mAb) plus complement (C) (T^– chimeras) and BM chimeras which had been reconstituted with BM cells pretreated with anti-Thy-1 mAb alone (T⁺ chimeras). When lethally irradiated AKR (Mls-1^a) mice were reconstituted with BM cells from B10 or B10 H-2 congenic mice, both T⁺ and T^– chimeras were entirely free of signs of graft-versus-host reaction (GVHR). However, complete replacement of the AKR lymphoid tissues by donor BM cells was accomplished at an early stage in T⁺ chimeras but not in T^– chimeras. On the other hand, clonal elimination of Vβ6⁺ T cells reactive to the recipient Ag (Mls-1^a) was abolished in T⁺ chimeras but successfully induced in T^– chimeras. The Vβ6⁺ T cells not eliminated in T⁺ chimeras showed depressed responses against Mls-1^a antigens. The findings herein demonstrate that T cells which contaminate a BM inoculum survive in recipient mice after treatment with anti-Thy-1 mAb without C in vitro followed by BMT. The surviving T cells have been estimated to represent fewer than 0.5% of the BM cells inoculated. These cells appear to accelerate the full replacement of recipient lymphoid tissues by donor cells. Furthermore, the T cells which survive in the marrow inoculum influence eventually the development of a tolerant state in the T cell repertoire of the donor.