A developing paradigm for the development of bird beaks

Some adaptive radiations are notable for extreme interspecific diversification in one or a few adult traits. How and why have trait differences evolved? Natural and sexual selection often provide answers to the question of why. An answer to the question of how is to be found in the genetic control of the phenotypic traits, especially in the early stages of development, when interspecific differences first become expressed. Recent studies of the molecular genetic control of beak development in Darwin's finches have shown that a signalling molecule (BMP4) plays a key role in the development of large and deep beaks. Expression of this molecule occurs earlier (heterochrony) and at higher levels in species with deep beaks compared with species with more pointed beaks. The implication of this finding is that variation in the regulation of one or a few genes that are expressed early could be the source of evolutionarily significant variation that is subject to natural selection in speciation and adaptive radiation. This view is reinforced by parallel findings with the same signalling molecule in the development of jaw morphology in cichlid fish of the Great Lakes of Africa. Further research into regulatory mechanisms is to be expected, as well as extension to other examples of radiation such as honeycreepers in Hawaii and Anolis lizards in the Caribbean. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88 , 17–22.     

Non-random distribution among a guild of parasitoids: implications for community structure and host survival

Abstract 1. Immature stages of the gall midge, Asphondylia borrichiae, are attacked by four species of parasitoids, which vary in size and relative abundance within patches of the gall midge’s primary host plant, sea oxeye daisy (Borrichia frutescens). 2. In the current study, a bagging experiment found that the smallest wasp, Galeopsomyia haemon, was most abundant in galls exposed to natural enemies early in the experiment, when gall diameter is smallest, while the wasp with the longest ovipositor, Torymus umbilicatus, dominated the parasitoid community in galls that were not exposed until the 5th and 6th weeks when gall diameter is maximal. 3. Moreover, the mean number of parasitoids captured using large artificial galls were 70% and 150% higher compared with medium and small galls respectively, while stem height of artificial galls significantly affected parasitoid distribution. Galls that were level with the top of the sea oxeye canopy captured 60% more parasitoids compared with those below the canopy and 50% more than galls higher than the plant canopy. 4. These non‐random patterns were driven primarily by the differential distribution of the largest parasitoid, T. umbilicatus, which was found significantly more often than expected on large galls and the smallest parasitoid of the guild, G. haemon, which tended to be more common on stems level with the top of the plant canopy. 5. Large Asphondylia galls, especially those located near the top of the Borrichia canopy, were more likely to be discovered by searching parasitoids. Results using artificial galls were consistent with rates of parasitism of Asphondylia galls in native patches of sea oxeye daisy. Gall diameter was 19% greater and the rate of parasitism was reduced by almost 50% on short stems; as a result, gall abundance was 24% higher on short stems compared with ones located near the top of the plant canopy. 6. These results suggest that parasitoid community composition within galls is regulated by both interspecific differences in ovipositor length and preferences for specific gall size and/or stem length classes.     

Infestation of commercial bumblebee (Bombus impatiens) field colonies by small hive beetles (Aethina tumida)

Abstract.  1. The small hive beetle, Aethina tumida , is a parasite of honeybee ( Apis mellifera ) colonies native to sub-Saharan Africa and has become an invasive species. In North America the beetle is now sympatric with bumblebees, Bombus , not occurring in its native range. Laboratory studies have shown that small hive beetles can reproduce in bumblebee colonies but it was not known whether infestations occur in the field.
2. For the first time, infestation of bumblebee colonies by small hive beetles was investigated in the field. Commercial Bombus impatiens colonies ( n = 10) were installed in proximity to infested apiaries. Within 8 weeks, all colonies that were alive in the 5-week observation period ( n = 9) became naturally infested with adult small hive beetles and successful small hive beetle reproduction occurred in five colonies.
3. In four-square choice tests, the beetles were attracted to both adult bumblebee workers and pollen from bumblebee nests, suggesting that these odours may serve as cues for host finding.
4. The data indicate that bumblebee colonies may serve as alternative hosts for small hive beetles in the field. To foster the conservation of these essential native pollinators, investigations on the actual impact of small hive beetles on wild bumblebee populations are suggested.     

Phylogeography of two parthenogenetic sawfly species (Hymenoptera: Tenthredinidae): relationship of population genetic differentiation to host plant distribution

This study compares the population genetic structure of two obligate parthenogenetic sawfly species, Aneugmenus padi (L.) Zhelochovtsev and Eurhadinoceraea ventralis (Panzer) Enslin (Hymenoptera: Tenthredinidae). Allozymes were used to detect genetic differences in larvae collected at different sites in six European countries. For A. padi , scoring six polymorphic enzymes revealed the existence of five dominant, widely distributed clones and several more with only very few individuals occurring locally. The clonal diversity and identity differed across collection sites, with up to at maximum eight clones coexisting at a single locality. In contrast, in E. ventralis , individuals from different localities were all monomorphic for at least six different enzymes and are therefore assumed to belong to the same clone. Differences in population genetic structure of these sawfly species can be related to the differing distributions of their host plants: the fern, Pteridium aquilinum , the host of A. padi , has been an invasive species for more than two hundred years. Spread of clones of A. padi is likely to have closely followed the complex invasive pattern of spread of the plant. Larvae of E. ventralis were collected from local, horticultural plantings of Clematis spp. of recent origin probably with gardeners having traded plants infested with the sawfly.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 219–227.     

Hesperotestudo (Testudines: Testudinidae) from the Pleistocene of Bermuda, with comments on the phylogenetic position of the genus

A recently discovered fossil land tortoise (Testudines: Testudinidae) is described from the Pleistocene of Bermuda. Its morphology is sufficiently well preserved to allow assignment to the extinct North American genus Hesperotestudo. However, several features of this tortoise are unique and it is named Hesperotestudo bermudae sp. nov. A review of the phylogenetic relationships of the better known genera of the Testudinidae suggests that the affinities of Hesperotestudo lie with other North American tortoises (Gopherus) and not with Geochelone or other testudinines; thus, Hesperotestudo is reassigned to the Xerobatinae. This is at least the fifth documentation of a testudinid dispersing over open ocean to an oceanic island (the first for Hesperotestudo) and it corroborates the hypothesis that members of this family are well suited to over-water dispersal.     

Influence of an ecosystem engineer,the emergent macrophyte Sparganium erectum,on seed trapping in lowland rivers and consequences for landform colonisation

1. Plant physical ecosystem engineers can influence vegetation population and community dynamics by modifying, maintaining or creating habitats. They may also have the potential to act upon biotic processes, such as seed dispersal. 2. Examples exist of reduction in seed dispersal distances in vegetated compared to unvegetated terrestrial environments, and concentration of seed deposits associated with plant patches. Such effects in aquatic environments have been little studied, but the engineering effect of plant patches on patterns of flow velocity and sediment deposition in streams suggests that they may play a similar role. 3. In this study, we assess the potential of an emergent aquatic species, Sparganium erectum, to play a role in physically modifying river habitats and trapping seeds by examining patterns of seed deposition and substrate type in 47 river reaches across England and southern Scotland, U.K. 4. Areas of the river channel within or adjacent to S. erectum patches harboured more plant seeds and more species than unvegetated areas and had finer, sandier substrates with higher organic matter, total nitrogen and total phosphorus content. Most seed species were competitive, indicating that they were well suited to colonise the competitive environment of an S. erectum patch, and could potentially further stabilise accumulated sediments and contribute to landform development. 5. We demonstrate that S. erectum patches influence both the physical environment and the retention of seeds, in consistent patterns across the channel bed, for a range of lowland rivers that vary in stream power and geology and which can be expected to vary in levels of supply of fine sediment and seeds. 6. Our findings support the hypothesis that the fundamental influence of a riverine ecosystem‐engineering species on slowing fluid flow links the habitat creation process of sediment sorting and retention to seed trapping. We suggest the process is applicable to a wide range of aquatic and riparian vegetation. We also suggest that the mono‐specific and competitive growth, which is typical of these engineering species, will strongly influence the recruitment of trapped seeds.     

Do parasitic flies attack mites? Evidence in Baltic amber

We provide the first evidence of a small-headed fly planidium (first instar larva; Diptera: Acroceridae) associated with a whirligig mite (Acari: Acariformes: Prostigmata: Anystina: Anystidae) in Baltic amber. This fossil is surprising as parasitic nematodes are the only metazoans known to successfully attack acariform mites, and Acroceridae are believed to be host-restricted parasitoids of spiders. The fossil corroborates a previously published, but widely dismissed, paper that first reported parasitism of parasitengone mites by acrocerid planidia. The possible natural history implications of this find are discussed.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 9–13.     

Bridging the morphological and biological species concepts: studies on the Bactrocera dorsalis (Hendel) complex (Diptera: Tephritidae: Dacinae) in South-east Asia

Defining species accurately is a critical need in fundamental disciplines such as ecology and evolutionary biology and in applied arenas such as pest management. The validity of species designations depends on agreement of different methods of species diagnosis for unique biological species. The Bactrocera dorsalis complex of fruit flies provide an excellent opportunity for such a test of the congruence of different techniques (e.g. morphological, molecular, host-plant based, chemotaxonomy) used for species diagnosis. The complex contains a large number of closely-related species, is distributed over a wide geographical range in South-east Asia and considerable information has been compiled on some species. In the present study, the morphological and biological species boundaries were compared using new data from morphometric analyses of reproductive and body parts, together with a review of data on morphology, chemistry of male pheromones that are important in courtship and mating, molecular analyses, and endemic rainforest host plants. For the populations studied ( Bactrocera carambolae , Bactrocera dorsalis , Bactrocera occipitalis , Bactrocera papayae , Bactrocera philippinensis , Bactrocera kandiensis and Bactrocera invadens ) there appears to be significant congruence between the morphological and biological species boundaries.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 217–226.     

An artificial intergeneric hybrid derived from sexual hybridization between the distantly related Arabidopsis thaliana and Pachycladon cheesemanii (Brassicaceae)

An artificial intergeneric hybrid derived from sexual hybridization between Arabidopsis thaliana (female) and Pachycladon cheesemanii (male) is characterized and formally named as ×Pachydopsis hortorum. A hybrid origin for ×Pachydopsis is supported by a chromosome number of 2n = 15, with this comprising haploid gametes from A. thaliana (n = 5) and P. cheesemanii (n = 10). DNA fingerprinting using amplified fragment length polymorphism data also confirmed the parentage of the hybrid, as it comprised the additive total of all of the fragments scored for P. cheesemanii and most of those scored for A. thaliana. ×Pachydopsis is a robust perennial herb with numerous leafy rosettes and long inflorescences like P. cheesemanii, and floral parts that are intermediate between the parents. ×Pachydopsis produces sterile pollen. Female function of ×Pachydopsis is partially normal, with the pollen of A. thaliana and several species of Pachycladon readily germinating on the stigma, and pollen tubes growing down the style and transmission tissue into the ovary. No seed was formed from these pollinations, although one embryo developed but subsequently aborted at the torpedo stage. Colchicine was used to induce polyploid inflorescences, and these were confirmed by the size and density of the stomata and pollen diameter. Flowers from the polyploid inflorescences of ×Pachydopsis were backcrossed with A. thaliana Landsberg erecta and 11 seeds were produced. Four backcross hybrid plants were raised and two of these had a chromosome number of 2n = 20, consistent with a haploid gamete (n = 15) from polyploid × Pachydopsis being fertilized by a haploid pollen gamete (n = 5) from A. thaliana Landsberg erecta. Polyploid × Pachydopsis flowers backcrossed with P. cheesemanii and crossed with P. novae‐zelandiae did not produce any seeds. The partially fertile intergeneric hybrid described here between Arabidopsis and Pachycladon is remarkable in that, although the two genera occur in an Arabidopsoid clade, they are separated by a reasonable phylogenetic distance. This relationship suggests that Pachycladon and ×Pachydopsis have the potential to be employed in the study of evolutionary and ecological processes using the wide array of Arabidopsis resources. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 533–544.