Trochophore concepts: ciliary bands and the evolution of larvae in spiralian Metazoa

‘Trochophore’ is a term used in a strict sense for larvae having an opposed-band method of feeding, involving a prototroch and metatroch. Other ciliary bands such as a telotroch and neurotroch may be present. The trochophore has been proposed to represent the ancestral larval form for a group of metazoan phyla (including all members of the Spiralia). The name trochophore is also often applied to larvae that do not conform to the above definition. A cladistic analysis of spiralian taxa (with special reference to polychaete annelids), based on a suite of adult and larval characters, is used to assess several hypotheses: (1) that the trochophore (in a strict sense) is a plesiomorphic form for the Spiralia; (2) that die stricdy defined trochophore is plesiomorphic for members of the Spiralia such as the Polychaeta. The homology of each of the various separate ciliary bands of spiralian larvae, and features such as the apical tuft and protonephridia is also assessed. The results favour the conclusion that the trochophore, if defined as a feeding larval form using opposed bands, should not be regarded as an ancestral (= plesiomorphic) type for the Spiralia, or any other large taxon such as the Polychaeta or Mollusca. The evidence suggests that the various ciliary bands have differing evolutionary histories, and only the Echiura (possibly an annelid group) has members with the classical trochophore. The trochophore is re-defined as a larval form with a prototroch. This broad definition covers a wide variety of larvae, and matches the current usage more accurately than the restricted term. Features such as the neurotroch, telotroch and opposed-band feeding show convergence and reversals. The nature of the metatroch requires further investigation. The presence of a prototroch (and hence trochophore larvae) is used to identify an apomorphy-based taxon, Trochozoa, that includes the first ancestor to have evolved a prototroch and all its descendants. This minimally includes the Annelida [sensu lato), Echiura, Entoprocta, Mollusca and Sipuncula and is a less inclusive taxon than the Spiralia.     

The rapid effects of a whole-lake reduction of coarse woody debris on fish and benthic macroinvertebrates

1. Ecosystems can enhance the biodiversity of adjacent ecosystems through subsidies of prey, nutrients and also habitat. For example, trees can fall into aquatic ecosystems and act as a subsidy that increases aquatic habitat heterogeneity. This habitat subsidy is vulnerable in lakes where anthropogenic development of shorelines coincides with a thinning of riparian forests and the removal of these dead trees (termed coarse woody debris: CWD). How the disruption of this subsidy affects lake ecosystems is not well understood.
2. We performed a whole ecosystem experiment on Little Rock Lake, a small (18 ha), undeveloped, and unfished lake in Vilas County, WI, U.S.A., that is divided into two similar-sized basins by a double poly-vinyl chloride curtain that prevents both fish and water exchange between basins. In 2002, we removed about 70% of the littoral CWD in the treatment basin, while the reference basin was left unaltered. We tested for changes in both fish and benthic macroinvertebrate community composition in the two years following the CWD reduction.
3. Yellow perch ( Perca flavescens ) was the most abundant fish species in the lake prior to our experiment, but declined to very low densities in the treatment basin after manipulation. We found no evidence of an effect on macroinvertebrates – the treatment basin's macroinvertebrate community composition, diversity and density did not change relative to the reference basin.
4. Our results indicate that different trophic groups may have differential responses to the loss of a habitat subsidy, even if anthropogenic effects on that subsidy are severe. In the case of Little Rock Lake, fish community responses were evident on a short-time scale, whereas the macroinvertebrate community did not rapidly change following CWD reduction.     

Respiration during the metamorphosis of sexuals in Lasius flavus (Hymenoptera, Formicidae)

ABSTRACT. The respiration of metamorphosing gyne Lasiusflavus Fab. has been measured in field and laboratory populations. Twelve morphological stages are identified and their respiratory rate investigated. Only five physiological phases are distinguished. The specific respiratory rate varies between these phases, to produce the U-shape characteristic of insects. There is good agreement between the data from English field and Danish laboratory populations. The minimum rate is only 40% of the maximum. Except at the beginning and end of metamorphosis, the Q₁₀ is significantly different in the two temperature intervals 10–20 and 20–30C. Metamorphosis was completed in approximately 33 days at 20C. The total oxygen consumption by the gynes during metamorphosis was 2.4 ml. Their weight loss amounted to 2.2 mg, or 36% of the dry weight and, of this, 0.67mg was accounted for by fat. Assuming the rest was carbohydrate, consumption of these reserves would release 62.9 J, which, for this combination of fat and carbohydrate, can be calculated to be equivalent to 3.1 ml oxygen which is in reasonable agreement with the figure calculated from the measurement of oxygen consumption. The specific respiratory rate in English field populations of male pupae varies in the same way as the gyne-pupae, but it is about 50% higher.     

Mammal responses to matrix development intensity

The landscape matrix is increasingly being recognized as important to biodiversity conservation. The nature of the matrix impacts the persistence of species in human‐modified landscapes through its pervasive influence on adjacent habitat and through the habitat value of the matrix itself. However, previous studies have not isolated the effects of the matrix from the effects of other aspects of landscape modification, such as habitat loss and fragmentation, and much remains to be understood about the independent impact of the matrix on wildlife. We investigated the effects of the matrix on mammal abundance and landscape use in south‐east Queensland, Australia. Mammals were surveyed in patch ‘core’, patch ‘edge’ and ‘matrix’ landscape elements along a rural–suburban gradient of matrix development intensity quantified by a weighted road‐length metric, which was significantly correlated with housing density, while controlling for potentially confounding patch and landscape attributes. Response to increasing matrix development intensity was highly species‐specific. Several native species declined in abundance; however, others were more resilient to moderate levels of matrix intensity, one species increased in abundance, and at least one species appeared unaffected by matrix intensity. Native species richness peaked at moderate levels of matrix development intensity. Exotic species richness and feral predators increased with matrix intensity and were negatively correlated with native species. Species response to matrix intensity appeared related to their use of edge or matrix habitat. An ability to use the matrix per se, however, may not translate into an ability to persist in a landscape where development substantially reduces the habitat or movement value of the matrix.     

Broadcasting fables: Is external fertilization really primitive? Sex,size, and larvae in sabellid polychaetes

Traditionally, broadcast spawning and planktonic larvae have been considered the plesiomorphic ‘ground plan’ for the Polychaeta and other metazoan groups. To assess whether this reproductive mode is in fact ‘primitive’, the study of monophyletic groups with various reproductive modes should be informative. A large range of body sizes would allow testing the ideas that aspects of reproductive mode may be functionally constrained. The family Sabellidac is one such group, with sexual reproductive modes ranging from broadcast spawning to intratubular brooding to ovovivi-parity, and a body size range over more than five orders of magnitude. Sabellids have previously been the subject of detailed cladistic analyses (Fitzhugh 1989, 1991); here we introduce several new characters based on morphology of reproductive structures. Larval development in four brooding sabellid species is also described with the aim of introducing new characters for future systematic analyses. Our cladistic analysis of sabellid genera suggests that gonochorism and brooding of direct-developing larvae are plesiomorphic in the Sabellidae, with external fertilization and swimming larvae limited to apomorphie clades in the subfamily Sabellinae. The presence of sperm with elongate heads may be correlated with the presence of intratubular brooding, though an adequate causal explanation for this relationship can not yet be presented. The concept that ‘modified’ sperm must be derived from ‘primitive’ sperm is shown to be false, with ‘modified’ sperm being plesiomorphic for the Sabellidae, from which ‘primitive’ sperm is derived in apomorphic Sabellinae. All sabellids have lecithotrophic development and appear to be phylogenetically constrained in this regard. Data gathered on body size and reproductive variables in the Sabellidac suggests the following (when phylogenetic effects are not controlled): (1) egg number and total egg volume are significantly correlated with body size, with small animals having fewer, larger eggs than large animals; (2) individual egg volume is not correlated with body size; (3) reproductive mode is significantly correlated with body size; intratubular brooders tend to be small-bodied, whereas broadcast spawners are large. However when the effect of body size is controlled for, then (4) egg number, egg volume and total egg volume all vary significantly with reproductive mode. Broadcast spawners expel a large number of small eggs for a high total egg volurne. Intratubular brooders have a few relatively large eggs for a small total egg volume. When statistics arc performed using phylogenetically independent contrasts there is a significant correlation between total egg volume and body size but not for egg number and body size. The effect of non-independence (due to phylogeny) of our data needs to be more fully controlled in future analyses but methods of incorporating continuous data into cladistic analyses should also be investigated. We show that some predictions can be made about reproductive mode based on body size but ad hoc patterns of reproductive character-state transformation should not be made independent of empirical hypotheses of phylogenetic relationship. Further studies of this kind throughout the Annelida are needed to determine the plesiomorphic reproductive mode for the phylum.     

Polychaete systematics: Past and present

In this paper, we first demonstrate the historical background for the current unsatisfactory state of systematics of the polychaetes. We then briefly discuss our knowledge of internal and external structures. A review of the polychaete families makes up the third section; 81 families are treated in detail. Five families have been recently synonymized with others, and six families are too poorly known to be sufficiently characterized. Fossil polychaetes are briefly mentioned, with specific attention to problems associated with incorporating them in recent systematics.
The traditional separation in 'errant' and 'sedentary' polychaetes has increasingly become recognized as being unsatisfactory; however, the current trend towards grouping the polychaetes in many orders without specifying the relationships among the orders, is no more satisfactory. The lack of consistent morphological information is a major source of uncertainty. Intensive morphological studies should remove terminological ambiguities and alleviate some of the problems.     

Vrijenhoekia balaenophila, a new hesionid polychaete from a whale fall off California

Vrijenhoekia balaenophila gen. nov., sp. nov. (Polychaeta, Hesionidae) is described from a whale carcass at near 3000 m depth in Monterey Canyon off the coast of California. The phylogenetic relationships of V. balaenophila are assessed in a parsimony analysis of morphological data together with nucleotide data from 28S rDNA, 16S rDNA and cytochrome oxidase I genes. Within the hesionids V. balaenophila belongs to Psamathini, where it is the sister group to Sirsoe . Among psamathins it is morphologically distinguished by having six glandular lip pads around the mouth opening, papilla-shaped neuropodial lobes on segment 3, extreme length of the dorsal cirri, and by a characteristic growth pattern in which the maximum number of segments is already formed in subadults, and further growth takes place through size increase of the segments.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 625–634.     

State and change in carbon pools in the forests of tropical Africa

To improve estimates of the state and change in C pools due to changes in land use in tropical forests of Africa, we combined spatially explicit estimates of biomass C density, obtained by modelling in a geographical information system (GIS), with new data on the area of forests (woody formations with a minimum of 10% crown cover) reported at subnational units for 1980 and 1990 by the Food and Agriculture Organization (FAO). Estimates of the biomass C densities for grass/shrub savannas were also included using a simple model based on precipitation. The total C pool in above– and below–ground forests and grass/shrub savannas of Africa for 1980 was 50.8 Pg (10¹⁵g), with aboveground forest biomass accounting for 75% of the total, below–ground forest biomass for 21%, and grass/shrub savannas for 4%. Area weighted mean biomass C densities were about 180 Mg ha^–1 for lowland moist forests, 82 Mg ha^–1 for all forests, and 6 Mg ha^–1 for grass savannas. The total change in the aboveground forest C pool for the decade 1980–90 due to changes in land cover and use was estimated to be a decrease of 6.6 Pg C. Of this total, 43% was due to deforestation and 57% due to biomass reduction by other human activities. Six countries, mostly in central Africa, accounted for more than 73% of the total change in the C pool. The difference between state and change of C pool estimates made at the subnational scale and those made at the national scale proved to be insignificant across the region as a whole (2% for pools and – 1% for change in pool) but potentially important to individual countries (from + 36% to – 39% for pools and from + 43% to – 57% for change in pool). The differences between the two approaches may reflect a better match of the areas being deforested with the biomass C density of forests being cleared.