Ultrastructural Investigation of the Integument of Tubiluchus philippinensis (Priapulida, Tubiluchidae)

The integument of Tubiluchus philippinensis van der Land, 1984 has been investigated by means of scanning and transmission electron microscopy. The ultrastructure of the cuticle corresponds principally to what has been found in Priapulidae. The tumuli are mere cuticular thickenings. Setae, tubuli, flosculi and scalids are receptor organs. Tubuli additionally serve a second function: they produce a secretion. The male genital area is equipped with various receptor organs, the internal morphology of which has been described. All receptor cells are characterized by apical cilia, which may be surrounded by a circlet of microvilli. They sometimes bear a rather complicated rootlet apparatus.     

Contributions of Comparative Ultrastructural Research to Problems of Invertebrate Evolution

The contributions of ultrastructural research to the elucidationof invertebrate evolution are discussed by means of a numberof selected examples. Studies of the fine structure of the integumentof Aschelminthes and Platyhelminthes illustrate the method ofinterpretation. In addition, the following subjects and theirsignificance for phylogeny are treated: annelid setae, sensillaof Pentastomida, choanocyte-like cells, epitheliomuscular cells,podocytes, gills of Polychaeta and lungs of Decapoda, and spermatozoa     

Temperature cues phenological synchrony in ant‐mediated seed dispersal

Species‐specific climate responses within ecological communities may disrupt the synchrony of co‐evolved mutualisms that are based on the shared timing of seasonal events, such as seed dispersal by ants (myrmecochory). The spring phenology of plants and ants coincides with marked changes in temperature, light and moisture. We investigate how these environmental drivers influence both seed release by early and late spring woodland herb species, and initiation of spring foraging by seed‐dispersing ants. We pair experimental herbaceous transplants with artificial ant bait stations across north‐ and south‐facing slopes at two contrasting geographic locations. This use of space enables robust identification of plant fruiting and ant foraging cues, and the use of transplants permits us to assess plasticity in plant phenology. We find that warming temperatures act as the primary phenological cue for plant fruiting and ant foraging. Moreover, the plasticity in plant response across locations, despite transplants being from the same source, suggests a high degree of portability in the seed‐dispersing mutualism. However, we also find evidence for potential climate‐driven facilitative failure that may lead to phenological asynchrony. Specifically, at the location where the early flowering species (Hepatica nobilis) is decreasing in abundance and distribution, we find far fewer seed‐dispersing ants foraging during its fruit set than during that of the later flowering Hexastylis arifolia. Notably, the key seed disperser, Aphaenogaster rudis, fails to emerge during early fruit set at this location. At the second location, A. picea forages equally during early and late seed release. These results indicate that climate‐driven changes might shift species‐specific interactions in a plant–ant mutualism resulting in winners and losers within the myrmecochorous plant guild.     

Efficiency of selection, as measured by single nucleotide polymorphism variation, is dependent on inbreeding rate in Drosophila melanogaster

It is often hypothesized that slow inbreeding causes less inbreeding depression than fast inbreeding at the same absolute level of inbreeding. Possible explanations for this phenomenon include the more efficient purging of deleterious alleles and more efficient selection for heterozygote individuals during slow, when compared with fast, inbreeding. We studied the impact of inbreeding rate on the loss of heterozygosity and on morphological traits in Drosophila melanogaster. We analysed five noninbred control lines, 10 fast inbred lines and 10 slow inbred lines; the inbred lines all had an expected inbreeding coefficient of approximately 0.25. Forty single nucleotide polymorphisms in DNA coding regions were genotyped, and we measured the size and shape of wings and counted the number of sternopleural bristles on the genotyped individuals. We found a significantly higher level of genetic variation in the slow inbred lines than in the fast inbred lines. This higher genetic variation was resulting from a large contribution from a few loci and a smaller effect from several loci. We attributed the increased heterozygosity in the slow inbred lines to the favouring of heterozygous individuals over homozygous individuals by natural selection, either by associative over‐dominance or balancing selection, or a combination of both. Furthermore, we found a significant polynomial correlation between genetic variance and wing size and shape in the fast inbred lines. This was caused by a greater number of homozygous individuals among the fast inbred lines with small, narrow wings, which indicated inbreeding depression. Our results demonstrated that the same amount of inbreeding can have different effects on genetic variance depending on the inbreeding rate, with slow inbreeding leading to higher genetic variance than fast inbreeding. These results increase our understanding of the genetic basis of the common observation that slow inbred lines express less inbreeding depression than fast inbred lines. In addition, this has more general implications for the importance of selection in maintaining genetic variation.     

Systematic review of a new orb‐weaving spider genus (Araneae: Araneidae), with special reference to the Australasian‐Pacific and South‐East Asian fauna

The Australasian‐Pacific and South‐East Asian species of the new orb‐weaving spider genus Plebs with Plebs eburnus (Keyserling, 1886) as type species are revised. Following this study, Plebs includes a total of 22 species of which seven are here described new. Seven species are found in Australia, two in the Pacific region (New Caledonia, Vanuatu), and two in South‐East Asia (Papua New Guinea, The Philippines). Eleven Asian species are transferred to the new genus. Plebs represent comparatively small orb‐weaving spiders of c. 1.2–15.0 mm body length with a slightly elongated abdomen and humeral (shoulder) humps. Males of most species have two to three stout setae on the ventral side of their fourth coxae. Male pedipalps are characterized by the presence of a single macroseta on the patella, the presence of a paramedian apophysis as basal extension of the conductor, and an apical tegular protrusion. The female epigyne has a scape that is generally much longer than wide. It does not have a terminal pocket and is frequently broken off in a number of species. A phylogenetic analysis of 15 species of Plebs (those for which both sexes are known), 13 Australian/Pacific orb‐weaving spider species representing the most commonly collected clades with paramedian apophysis, three species of Nearctic Eriophora Simon, 1864, and Araneus diadematus Clerck, 1758, as outgroup, identified a single synapomorphy of Plebs based on 35 morphological and three behavioural characters: a distinct, inverted U‐shaped light pattern on the ventral side of the abdomen with two additional white spots anterolateral to the spinnerets. This analysis recovered a monophyletic clade of all Asian Plebs, suggesting a single colonization event of the genus that putatively originated in Australia. Most Plebs species appear to be active during the day. They build a regular orb‐web with vertical stabilimentum in grass and low shrubs. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 279–341.     

Spatio-temporal population genetics of the Danish pine marten (Martes martes)

A spatio-temporal study of genetic variation in the Danish pine marten ( Martes martes ) populations from the Jutland peninsula and from the island of Sealand was performed using 11 microsatellite markers. Samples obtained from 1892 to 2003 were subdivided into historical (prior to 1970) and recent (from 1970) groups. As compared with the historical samples, there was a significant loss of genetic variation in the recent Jutland population, but not in Sealand. Effective population sizes were estimated using Bayesian-based software (TMVP). Historical effective population sizes were 5897 (90% highest probability density, HPD, limits: 1502–6849) in Jutland and 1300 (90% HPD limits: 224–5929) in Sealand, whereas recent effective population sizes were 14.7 (90% HPD limits: 10.9–23.5) in Jutland and 802 (90% HPD limits: 51.8–5510) in Sealand. Significant genetic differentiation ( F _ST) was found between the two historical samples, between the two recent samples, and between the historical and the recent sample in Jutland; whereas the F _ST value between the historical and the recent sample in Sealand was not significant. The significant genetic differentiation between the historical and the recent samples indicates changes in the genetic compositions over time, and the higher F _ST values between the two recent samples, as compared with the two historical samples, indicates that the populations in Sealand and Jutland have drifted apart within a short time span. No deviation from Hardy–Weinberg equilibrium was found within populations, indicating no further substructuring.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 457–464.     

Microsatellite DNA analysis of northern pike (Esox lucius L.) populations: insights into the genetic structure and demographic history of a genetically depauperate species

The northern pike Esox lucius L. is a freshwater fish exhibiting pronounced population subdivision and low genetic variability. However, there is limited knowledge on phylogeographical patterns within the species, and it is not known whether the low genetic variability reflects primarily current low effective population sizes or historical bottlenecks. We analysed six microsatellite loci in ten populations from Europe and North America. Genetic variation was low, with the average number of alleles within populations ranging from 2.3 to 4.0 per locus. Genetic differentiation among populations was high (overall θ_ST = 0.51; overall ρ_ST = 0.50). Multidimensional scaling analysis of genetic distances between populations and spatial analysis of molecular variance suggested a single phylogeographical race within the sampled populations from northern Europe, whereas North American and southern European populations were highly distinct. A population from Ireland was monomorphic at all loci, presumably reflecting founder events associated with introduction of the species to the island in the sixteenth century. Bayesian analysis of demographic parameters showed differences in θ (a product of effective population size and mutation rate) among populations from large and small water bodies, but the relative differences in θ were smaller than expected, which could reflect population subdivision within the larger water bodies. Finally, the analyses showed drastic population declines on a time scale of several thousand years within European populations, which we ascribe to either glacial bottlenecks or postglacial founder events.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 91–101.