Effects of herbicide-tolerant transgenic oilseed rape genotypes on honey bees and other pollinating insects under field condtions

Abstract Various parameters of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), such as ovipositional behaviour, development period, and ability of newly hatched larvae to utilise the host for further growth, are affected by host attributes that could be physical or chemical in nature. These factors were assessed using green‐ and black‐gram (Leguminosae) seed characteristics to explore whether they affected oviposition behaviour, fecundity, and breeding success in C. maculatus, and to determine whether the presence of cysteine proteinase inhibitor (CPI) within the seeds caused inhibition of proteinase activity in C. maculatus. Investigation revealed that green‐gram (Vigna radiata (L.) Wilczek) varieties differed from black‐gram (Vigna mungo (L.) Hepper) varieties by having softer seeds with smoother seed coats. Green‐gram NM92 and the control had the heaviest seeds with the largest surface area and medium hardness, black‐gram had seeds with medium weight, medium surface area, and maximum hardness, and green‐gram NCM209 had the lightest seeds with smallest surface area and minimum hardness. Varieties with smooth seed coats and greater seed weight and surface area were preferred for oviposition. Grain texture was more important as an oviposition stimulus than grain surface area and size for the Islamabad biotype of C. maculatus. The level of CPI in seeds was not, on its own, responsible for the observed differences in insect development period or larval activity. Development period was shorter in green‐gram with softer seeds and was prolonged in black‐gram with harder seeds. Although C. maculatus did not suffer higher mortality in black‐gram seeds, the delay in development alone may lead to a considerable reduction in seed loss during storage, due to the low rate of multiplication and lower population growth.     

Genetic structuring in Andean landlocked populations of Galaxias maculatus: effects of biogeographic history

Aim To test whether the genetic diversity of diadromous and landlocked populations of the small puyen Galaxias maculatus (known as jollytail in Australia and inanga in New Zealand) follow the same structuring patterns observed for migratory and non‐migratory species of the genus Galaxias. This work also aimed to test whether the genetic structuring of a group of populations could be predicted from differences in the geomorphologic history of the region they inhabit. Location Eight landlocked populations were sampled from cold‐temperate lakes in north‐western Patagonia. The study area could be split latitudinally into two sectors that differed in their geomorphology, each of them hosting four populations. The southern sector shows evidence of a higher degree of glacial coverage, and the lakes are probably remnants of a big proglacial palaeolake. Lakes in the northern sector, on the other hand, suggest no common origin. Results Significant genetic structuring was found among the studied populations (Θ = 0.188), being the highest value reported to date for the species. Significant correlation was found between genetic diversity and lake area and perimeter. Diversity also showed a slight latitudinal variation suggesting the presence of genetically distinct groups of populations. The comparison of populations from the two geographical sectors showed that those from the north had a higher diversity, more private alleles and strong structuring, while those from the south were less diverse and much more homogeneous. Main conclusions Non‐migratory populations of G. maculatus show much higher values of genetic structuring than those reported for diadromous populations. This follows the pattern seen when comparing migratory and non‐migratory species of Galaxias. This agrees with population genetics theory which predicts that restricted gene flow would result in greater among‐population divergence. Also, differences between northern and southern populations agreed with what was predicted by the geomorphologic history of the study area. During the Last Glacial Maximum ice cover in that region may have reduced the habitat of G. maculatus to a refuge with an impoverished gene pool. When the ice receded, leaving a great proglacial lake, that former population expanded and became fragmented after water levels descended. This resulted in present day lakes harbouring homogeneous populations with reduced diversity. The northern sector, in contrast, was less affected by glaciers, resulting in more geomorphologically stable lakes holding genetically diverse populations.     

A comparison of nuclear and cytoplasmic genetic effects on sperm competitiveness and female remating in a seed beetle

It is widely assumed that male sperm competitiveness evolves adaptively. However, recent studies have found a cytoplasmic genetic component to phenotypic variation in some sperm traits presumed important in sperm competition. As cytoplasmic genes are maternally transmitted, they cannot respond to selection on sperm and this constraint may affect the scope in which sperm competitiveness can evolve adaptively. We examined nuclear and cytoplasmic genetic contributions to sperm competitiveness, using populations of Callosobruchus maculatus carrying orthogonal combinations of nuclear and cytoplasmic lineages. Our design also enabled us to examine genetic contributions to female remating. We found that sperm competitiveness and remating are primarily encoded by nuclear genes. In particular, a male's sperm competitiveness phenotype was contingent on an interaction between the competing male genotypes. Furthermore, cytoplasmic effects were detected on remating but not sperm competitiveness, suggesting that cytoplasmic genes do not generally play a profound evolutionary role in sperm competition.     

Phenotypic plasticity in a complex world: interactive effects of food and temperature on fitness components of a seed beetle

Most studies of phenotypic plasticity investigate the effects of an individual environmental factor on organism phenotypes. However, organisms exist in an ecologically complex world where multiple environmental factors can interact to affect growth, development and life histories. Here, using a multifactorial experimental design, we examine the separate and interactive effects of two environmental factors, rearing host species (Vigna radiata, Vigna angularis and Vigna unguiculata) and temperature (20, 25, 30 and 35°C), on growth and life history traits in two populations [Burkina Faso (BF) and South India (SI)] of the seed beetle, Callosobruchus maculatus. The two study populations of beetles responded differently to both rearing host and temperature. We also found a significant interaction between rearing host and temperature for body size, growth rate and female lifetime fecundity but not larval development time or larval survivorship. The interaction was most apparent for growth rate; the variance in growth rate among hosts increased with increasing temperature. However, the details of host differences differed between our two study populations; the degree to which V. unguiculata was a better host than V. angularis or V. radiata increased at higher temperatures for BF beetles, whereas the degree to which V. unguiculata was the worst host increased at higher temperatures for SI beetles. We also found that the heritabilities of body mass, growth rate and fecundity were similar among rearing hosts and temperatures, and that the cross-temperature genetic correlation was not affected by rearing host, suggesting that genetic architecture is generally stable across rearing conditions. The most important finding of our study is that multiple environmental factors can interact to affect organism growth, but the degree of interaction, and thus the degree of complexity of phenotypic plasticity, varies among traits and between populations.     

Reproductive interference in laboratory experiments of interspecific competition

Many studies that have researched interspecific competition in Callosobruchus (bean beetles), Drosophila (fruit flies), and Tribolium (flour beetles) have considered the major drivers of interspecific competition to be interspecific resource competition and intraguild cannibalism. These competition drivers have a density-dependent effect on the population dynamics. However, some studies have also detected a relative-frequency-dependent effect in the observed population dynamics. The most likely causal mechanism of this relative frequency dependence is reproductive interference, defined as any interspecific sexual interaction that damages female reproductive success. Reproductive interference has been overlooked by most laboratory studies in spite of the critical effect on the competition outcome. In this paper, I review laboratory studies of these insect genera from the perspective of reproductive interference and show that the reported results can be more reasonably interpreted by the joint action of reproductive interference and resource competition, including intraguild cannibalism. In addition, on the basis of results reported by a small number of related studies, I discuss the behavioral and evolutionary changes induced in those genera by reproductive interference.     

Vertical habitat shift of viviparous and oviparous deep‐sea cusk eels revealed by otolith microstructure and stable‐isotope composition

Otolith stable‐oxygen‐isotope composition and microstructure were analysed in order to investigate the vertical habitat shift of deep‐sea cusk eels (Ophidiiformes). Otolith δ¹⁸O profiles suggested that both viviparous blind cusk eels and oviparous cusk eels experienced a pelagic larval stage and then settled to the deep‐sea floor over a vertical distance that ranged among individuals from 200 to >1000 m. This result shows that the larvae of viviparous Barathronus maculatus undertake an ontogenetic vertical migration after a period of larval drift that may facilitate their wide distribution on the sea floor.     

No evidence for divergence in male harmfulness or female resistance in response to changes in the opportunity for dispersal

The outcome of sexual conflict can depend on the social environment, as males respond to changes in the inclusive fitness payoffs of harmfulness and harm females less when they compete with familiar relatives. Theoretical models also predict that if limited male dispersal predictably enhances local relatedness while maintaining global competition, kin selection can produce evolutionary divergences in male harmfulness among populations. Experimental tests of these predictions, however, are rare. We assessed rates of dispersal in female and male seed beetles Callosobruchus maculatus, a model species for studies of sexual conflict, in an experimental setting. Females dispersed significantly more often than males, but dispersing males travelled just as far as dispersing females. Next, we used experimental evolution to test whether limiting dispersal allowed the action of kin selection to affect divergence in male harmfulness and female resistance. Populations of C. maculatus were evolved for 20 and 25 generations under one of three dispersal regimens: completely free dispersal, limited dispersal and no dispersal. There was no divergence among treatments in female reproductive tract scarring, ejaculate size, mating behaviour, fitness of experimental females mated to stock males or fitness of stock females mated to experimental males. We suggest that this is likely due to insufficient strength of kin selection rather than a lack of genetic variation or time for selection. Limited dispersal alone is therefore not sufficient for kin selection to reduce male harmfulness in this species, consistent with general predictions that limited dispersal will only allow kin selection if local relatedness is independent of the intensity of competition among kin.     

Ability of ovipositing seed beetles to discriminate between seeds with differing egg loads

Abstract. 1. Previous work has shown that ovipositing females of Callosobruchus maculatus (F.) avoid seeds already bearing eggs, and thereby reduce competition among their larval progeny within seeds.
2. This study demonstrates that females also detect small differences in egg density, and prefer to oviposit on seeds with a lower-than-average number of eggs. A nearly uniform dispersion of eggs is thus maintained even after all seeds bear several eggs.
3. In addition, variation in egg load influences oviposition rate. Transfer of females from seeds with few eggs to seeds with many eggs inhibits oviposition; the reverse transfer stimulates it.
4. The upper surface of the egg chorion or egg 'cover' remains intact on the seed surface after the larva has entered the seed and continues to deter egg-laying for at least as long as the period required for larval development. 14-day-old egg covers provide as much deterrence as freshly laid eggs.