Mate choice in the brown thornbill (<Emphasis Type="Italic">Acanthiza pusilla</Emphasis>): are settlement decisions,divorce and extrapair mating complementary strategies?

In socially monogamous birds, females may express mate preferences when they first select a breeding partner, through divorce and subsequent breeding dispersal to a new partner and through extrapair mating. We examined settlement patterns, divorce and breeding dispersal in a sedentary Australian passerine, the brown thornbill (Acanthiza pusilla), in relation to two traits known to influence extrapair paternity (male age and male size). Settlement decisions, divorce and territory switching behaviour were all female strategies that reduced their likelihood of breeding with 1-year-old males. Females preferred to settle in territories with 2+ -year-old males, were more likely to divorce 1-year-old males, and only switched territories if they had an opportunity to form a new pair bond with an old male. In contrast, female settlement and divorce decisions were not influenced by male size. Female thornbills obtain a direct benefit from preferring older males as social mates because breeding success improves with male age in brown thornbills. Nevertheless, divorce rates in this species were low (14% of pair bonds were terminated by divorce), and individuals rarely switched territories following the death of a mate. Both of these mating strategies appeared to be primarily constrained by the distance adults moved to initiate a new pair bond (1–2 territories) and by the limited availability of unpaired older males in the immediate neighbourhood.Communicated by M. Webster     

Population genetic structure of the milkfish,<Emphasis Type="Italic"> Chanos chanos</Emphasis>, based on PCR-RFLP analysis of the mitochondrial control region

The milkfish, Chanos chanos (Forsskål, 1775) is a pelagic, monotypic gonorhynchiform widely distributed in the tropical Indo-Pacific. This study evaluates temporal variability of milkfish samples from the Philippine archipelago, and spatial variability at two geographic scales based on restriction fragment length polymorphism (RFLP) analysis of a portion of the mitochondrial control region. High levels of genetic diversity characterize the milkfish control region (mean h=0.908, =1.59%), with 74 haplotypes detected among the 367 fish analyzed. For temporal analysis of Philippine samples, milkfish were collected over 2 years from three sites (inter-annual variation), and sampled twice within a year during different seasons at four sites (intra-annual variation). No significant temporal variability was detected between or within years. Significant spatial differentiation among the Philippine samples was observed (F_ST=0.006, P<0.05), with two northeastern samples, Claveria and Dingalan, found to be genetically distinct. However, an hierarchical analysis of molecular variance (AMOVA), where samples were grouped into four geographic regions, revealed very low levels of genetic partitioning, with less than 1% of the total variation attributed to between-region differences, and lack of genetic structure. Nonetheless, the existence of putative northeastern Philippine populations is not discounted. Strong genetic structure across broad geographical scales was revealed by AMOVA, with 11% of the molecular variance based on haplotype frequencies allocated between three distinct groups: Indian Ocean, west Pacific (Philippines) and north central Pacific (Hawaii) The broad-scale genetic structure points to limited gene flow among disjunct Indo-Pacific populations.Communicated by T. Ikeda, Hakodate     

Temporal and spatial settlement patterns of sympatric hermit crabs and the influence of shell resource availability

Larvae of marine organisms often need specific resources or environments at settlement, and their success at settlement might be strongly influenced by the abundance and distribution of such specific resources. The larvae of hermit crabs need small shells to settle, so it is thought that the distribution and abundance of small shells influence the settlement pattern of hermit crabs. To investigate the influence of small shell distribution on the settlement of pagurid hermit crab larvae, we conducted a field experiment at an intertidal rocky shore in Hakodate Bay, Japan. From the line-transect sampling in the field, we found that Pagurus middendorffii settled extensively in the offshore side of the intertidal zone while P. nigrofascia settled in the uppermost area of the intertidal zone. Small shells were most abundant in a narrow shallow trough, slightly offshore from the uppermost area of the intertidal zone. For both species, settler abundance was high where adults were abundant, but settler abundance did not appear to be related to shells abundance. An experiment to clarify settlement patterns showed that larval recruits tended to be similar to those in the line-transect sampling of settlers. Thus shells may not be a primary factor affecting settlement patterns at relatively large scale within the intertidal flat. However, when we analyzed the relationship of settlers and shells separately within each transect, the distribution of settlers was well explained by shell resource availability. Therefore on a smaller scale, shell availability may influence the number of settlers. Settlement periods of P. middendorffii and P. nigrofascia fully overlapped, so their larvae probably were affected by similar transport factors, such as current and tidal movement. Nevertheless they showed different spatial patterns of settlement.Communicated by T. Ikeda, Hakodate     

Incorporation of pesticides by soil micro-organisms as a way of bound residues formation

We studied the ¹⁴C-tagged biochemical compartments such as proteins, lipids and polysaccharides from bacterial and fungal cultures supplied with ¹⁴C-pesticides and ¹⁴C-glucose. We showed that ¹⁴C incorporation depends both on the substrate structure and on the nature of the micro-organism. Both bacterial and fungal cells incorporated glucose ¹⁴C mainly into cell wall proteins. By contrast, glyphosate ¹⁴C was mainly incorporated into cytoplasm carbohydrates by fungi. On the other hand, 2,4-dichlorophenoxyacetic acid ¹⁴C was mainly found in the carbohydrate fractions of the bacteria walls.     

Male residence and the patterning of serum testosterone in vervet monkeys (<Emphasis Type="Italic">Cercopithecus aethiops</Emphasis>)

This study investigated hormonal and demographic processes underlying unimale and multimale mating systems in primates. Reproductive skew and challenge models of male competition provide conflicting predictions of the relationship of male residence to group composition and androgen regulation. These predictions were tested using endocrine and socioecological data from Kenyan vervet monkeys (Cercopithecus aethiops). Serum samples from 57 adult male monkeys, drawn from 19 separate groups and 4 populations, were assayed for testosterone by radioimmunoassay. Male ability to respond to conspecific challenge was assessed by their testosterone response to the capture protocol.Analyses showed that reproductive skew models were useful predictors of intergroup and interpopulation variation in male residence and T profiles. The Limited Control model of male residence was supported by positive correlations of the number of males per group with the number of females without dependent offspring, demonstrating that monopolization potential was a key determinant of male residence. Testosterone concentrations under conditions that elevated serum levels were positively correlated with infanticide risk, supporting the Concession model. Population comparisons provided evidence for increased T responsiveness where groups were predominantly unimale. Unimale populations were from sites with higher rainfall, suggesting that ecological factors contributed to population differences in male residence and T regulation.For species name, we follow the 2000 taxonomy of the IUCN/SSC Primate Specialist Groups workshop (Grubb et al. 2003)     

Territorial defense in a group-living solitary forager: who,where, against whom?

Territoriality is of great significance for many species and a characteristic of most group-living animals. Territoriality is thought to lead to increased reproductive success by defending a particular area containing critical resources. I describe several factors that influence territorial aggression in free-ranging striped mice (Rhabdomys pumilio), a group-living solitary forager. I induced territorial aggression by attracting mice of different groups using bait either at territory boundaries or in front of nests. Striped mice are territorial and make decisions about whether or not to attack a mouse from another group based upon several factors: (1) the sex of the opponent: males are much more likely to attack strange males than strange females, whereas no sex specific aggression was observed in females; (2) the body size of the opponent: striped mice are much more likely to attack a strange mouse that is lighter than themselves; and (3) the location of encounters: striped mice are much more likely to attack strangers, even those significantly heavier than themselves, in front of the nest than at territory boundaries. These variations in territorial responses between different types of individuals may be due to the different ultimate consequences of territorial aggression for different animals.Communicated by S. Alberts     

Sex ratio adjustment and maternal condition in two aphid species

We analyzed how offspring sex ratio varies with maternal condition in order to obtain evidence on the population structure in two aphid species with different life cycles. When fitness returns per unit investment differ for the production of daughters and sons, selection will favor an increasing investment into the sex with the higher returns. Therefore, the offspring sex ratios of individual mothers should become more biased towards the sex with the higher fitness returns as their condition or fecundity improves. The pattern of sex ratio adjustment we found in Uroleucon cirsii indicates local mate competition among males, while the pattern we found in Rhopalosiphum padi suggests local resource competition among sexual females. This might be the first evidence for local resource competition among females in an invertebrate species. Local mate competition means that fitness returns are limited by the availability of females as mates within local breeding groups, whereas local resource competition means that fitness returns are limited by the availability of resources for females competing within local groups. We discuss how the life cycles of both species fit to these hypotheses.