An unexpectedly sophisticated, V-shaped spermatozoon in Demospongiae (Porifera): reproductive and evolutionary implications

The demosponge Crambe crambe shows a peculiar spermatogenesis, hard to be reconciled with the basal position of sponges in the animal phylogeny. Early spermatogenesis stages showed most of the simple features expected in sponges. However, spermiogenesis departed from the anticipated process. Spermatids lengthened remarkably, forming a deep cytoplasmic pit around the cilium insertion, with the proximal axoneme bending to produce a V-shaped spermatozoon surprisingly similar to that known in the phylum Phoronida. The cytology was unexpectedly complex, with a needle-like nucleus of helically condensed chromatin, a conical acrosome with a subacrosomal rod, and a mitochondrion connected to the basal body by striated rootlets. These findings establish that the spermatozoon of broad-casting demosponges occurs in two structural categories ('primitive' and 'modified' type). This dualistic condition must necessarily have pre-dated the evolutionary apparition of higher metazoans, if we are to keep regarding sponges as the most primitive animals. We hypothesize that internal fertilization in C. crambe – and incidentally other demosponges – may depart from the general model assumed for spermcasting sponges. The V-shape of this spermatozoon suggests a design to favour autonomous penetration through the dense mesohyl to reach the oocytes, rather than engulfment and transportation by carrier cells towards the oocyte.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 413–426.     

Embryonic development of verongid demosponges supports the independent acquisition of spongin skeletons as an alternative to the siliceous skeleton of sponges

Approximately 85% of extant sponges (phylum Porifera) belong to the class Demospongiae, which contains 14 taxonomic orders. In the orders Verongida, Dictyoceratida, and Dendroceratida, jointly referred to as 'keratose demosponges', the skeleton does not contain siliceous spicules but only spongin fibres. This shared trait has encouraged placement of these orders together within Demospongiae, although their relationships remain uncertain. The present study documents for the first time embryo development in the order Verongida ( Aplysina aerophoba ), providing some clues for phylogenetic inference. Spawned eggs were enveloped by a follicle of maternal cells. Embryos and larvae were chimeric organisms, the blastocoel of which was filled with symbionts and maternal cells migrated from the follicle. The ultrastructure of epithelial larval cells revealed: (1) a basal apparatus characterized by a peculiar, angling accessory centriole; (2) a pear-shaped nucleus with a protruding beak connected to the rootlets of the basal body; and (3) a distinctive Golgi apparatus encircling the nuclear apex. Developmental and ultrastructural findings support the concept, in congruence with recent molecular studies, that Verongida are more closely related to Halisarcida (askeletal sponges) and Chondrosida (askeletal sponges + sponges with spongin + spiculate sponges) than to the remaining 'keratose' orders, making a monophyletic 'supra-ordinal unit' equivalent to a subclass (Myxospongia, new subclass). Hence, spongin skeletons have evolved at least twice in Demospongiae. Independent acquisition of 'corneous' materials as an alternative to silica could have been stimulated by the radiation of diatoms at the Cretaceous–Tertiary boundary (approximately 65 Mya), which depleted silicon in the photic zone of the world's ocean.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 427–447.     

Plankton response to weakening of the Iberian coastal upwelling

Coastal upwelling regions, which are affected by equatorward‐wind variability, are among the most productive areas of the oceans. It has been suggested that global warming will lead to a general strengthening of coastal upwelling, with important ecological implications and an impact on fisheries. However, in the case of the Iberian upwelling, the long‐term analysis of climatological variables described here reveals a weakening in coastal upwelling. This is linked to a decrease of zonal sea level pressure gradient, and correlated with an observed increase of sea surface temperature and North Atlantic Oscillation. Weakening of coastal upwelling has led to quantifiable modifications of the ecosystem. In outer shelf waters a drop in new production over the last 40 years is likely related to the reduction of sardine landings at local harbors. On the other hand, in inner shelf and Ria waters, the observed weakening of upwelling has slowed down the residual circulation that introduces nutrients to the euphotic layer, and has increased the stability of the water column. The drop in nutrient levels has been compensated by an increase of organic matter remineralization. The phytoplankton community has responded to those environmental trends with an increase in the percentage of dinoflagellates and Pseudonitzschia spp. and a reduction in total diatoms. The former favors the proliferation of harmful algal blooms and reduces the permitted harvesting period for the mussel aquaculture industry. The demise of the sardine fishery and the potential threat to the mussel culture could have serious socio‐economic consequences for the region.     

Riparian land use and the relationship between the benthos and litter decomposition in tropical montane streams

1. Although stream–catchment interactions have been analysed in some detail in temperate environments, little is known about the effects of land‐use changes in the tropics. Here, we analyse differences in benthic communities (macroinvertebrates and fungi) under two contrasting land uses (mature secondary forest and pasture) in montane streams in north‐western Ecuador and their influence on the rates of litter processing. 2. Between 2005 and 2006, we used a combination of coarse and fine mesh bags to study the relative contribution of macroinvertebrates and fungi to processing of two types of litter, Alnus acuminata and Inga spectabilis, in three‐first‐order streams running through mature secondary montane forests and adjacent downstream reaches running through pastures. At the same time, we characterised the assemblages of shreddering macroinvertebrates and fungi communities and the litter processing rates in stream reaches under both vegetation types. 3. Litter processing rates attributable to invertebrate feeding (coarse mesh bags) were significantly slower in streams running through pastures. Nevertheless, shredder diversity and richness were similar between pasture and forest sections, while shredder abundance was significantly higher in forest streams (mainly Phylloicus sp. :Trichoptera). Fungal reproductive activity and litter processing rates were low (fine mesh bags) and did not differ significantly between pasture and forest stream reaches. 4. Phylloicus sp. abundance was the best predictor of the percentage of litter remaining in coarse mesh bags across pasture and forest sites. Neither shredder diversity nor their species richness was a significant predictor of mass loss, as most of the decomposition was performed by a single keystone species. Although litter decomposition by microbial decomposers was low, fungal biomass (but not diversity) was the best variable explaining the percentage of litter remaining in fine mesh bags. 5. Our data suggest that, in these Neotropical montane streams, land use can have a significant impact on the rates of critical ecosystem processes, such as litter decomposition. In this study, this effect was not mediated by a major shift in the structure of the benthos, but by a decrease in the abundance and relative representation of a single species whose life history makes it critical to litter processing. 6. This study highlights the significant role that macroinvertebrate fauna can have in the processing of litter in Neotropical streams and the predominant role that single species can have in terms of controlling stream ecosystem‐level processes. Understanding the extent to which these patterns affect the long‐term and large‐scale functioning of stream ecosystems still needs further research and will become increasingly important in terms of managing lotic ecosystems in the context of rapid land‐use change.     

THE GENUS HAMINOEA (GASTROPODA: CEPHALASPIDEA) IN PORTUGAL, WITH A REVIEW OF THE EUROPEAN SPECIES

The study of specimens of Haminoea collected on the coast ofPortugal, together with the re-evaluation of historical specimensused by Nobre (1938–40) in his main work on the Portuguesemolluscs, recognized the presence of two species, Haminoea navicula(da Costa, 1778) and H. orbignyana (Férussac, 1822),and confirmed the misidentification of H. orbignyana as H. elegans(Gray, 1825). Anatomical analysis found intraspecific variabilityin the radula of H. navicula and H. orbignyana and in the seminalduct of the latter. The systematic value of taxonomic featuresincluding the shell, external morphology, animal coloration,radula, jaws, gizzard plates, prostate gland, seminal duct,penis and egg-masses is discussed. For all European speciesbut H. orbignyana, identification is only possible when anatomicaldata are considered, and the most relevant character is themale reproductive system. SEM images of the penis and prostateof H. navicula and H. orbignyana are given for the first time.A synoptic table for the recognition of the European speciesis provided. (Received 21 January 2005; accepted 17 June 2005)     

Habitat selection and diet of Western Capercaillie Tetrao urogallus in an atypical biogeographical region

Ecological features and conservation requirements of populations at the latitudinal limits of a species’ geographical range frequently differ from those in other parts of the range. Identifying such differences is key to implementing effective conservation strategies for threatened range‐edge populations especially, in the context of rapid global warming, at the lower‐latitude range edge. We studied habitat selection and diet of the endangered Cantabrian Capercaillie Tetrao urogallus cantabricus in a recently discovered population at the southernmost edge of the sub‐species’ range. This is the only Western Capercaillie population in the Mediterranean biogeographical region. We combined non‐systematic surveys based on questionnaires, reports and field sampling with data from radiotracking to assess habitat selection. Diet was surveyed by micro‐histological methods from droppings collected in the new population, which inhabits Pyrenean Oak Quercus pyrenaica forests and Scots Pine Pinus sylvestris plantations, and in two Cantabrian populations inhabiting Eurosiberian forests. Capercaillie preferred large (> 500 ha) and medium‐sized (100–500 ha) Pyrenean Oak forest fragments and large Scots Pine plantations. Forest fragments smaller than 100 ha and non‐forested habitats were always avoided. Diet differed markedly between Mediterranean and Eurosiberian populations. Bilberry Vaccinium myrtillus is common in the diet of most Capercaillie populations but was scarce in the study area and so was rare in the diet of the new population. Instead, Rockrose Halimium lasianthum was described for the first time as a major food resource for the Capercaillie and was consumed in autumn and winter. Pine needles were also heavily consumed in winter. We document for the first time the strong preference of Capercaillie for Pyrenean Oak forests and a moderately high consumption of the leaves, buds and acorns of this tree species throughout the year. Habitat selection and diet of this Mediterranean population differ from those of the core Cantabrian and other populations. Our results suggest a wider environmental tolerance (phenotypic plasticity) in the species than previously recognized. We advocate specific protection for this unique range‐edge Capercaillie population and its Pyrenean Oak forest habitat.     

Nestling coloration is adjusted to parent visual performance in altricial birds irrespective of assumptions on vision system for Laniidae and owls,a reply to Renoult et al.

We have recently published support to the hypothesis that visual systems of parents could affect nestling detectability and, consequently, influences the evolution of nestling colour designs in altricial birds. We provided comparative evidence of an adjustment of nestling colour designs to the visual system of parents that we have found in a comparative study on 22 altricial bird species. In this issue, however, Renoult et al. ( J. Evol. Biol., 2009 ) question some of the assumptions and statistical approaches in our study. Their argumentation relied on two major points: (1) an incorrect assignment of vision system to four out of 22 sampled species in our study; and (2) the use of an incorrect approach for phylogenetic correction of the predicted associations. Here, we discuss in detail re‐assignation of vision systems in that study and propose alternative interpretation for current knowledge on spectrophotometric data of avian pigments. We reanalysed the data by using phylogenetic generalized least squares analyses that account for the alluded limitations of phylogenetically independent contrasts and, in accordance with the hypothesis, confirmed a significant influence of parental visual system on gape coloration. Our results proved to be robust to the assumptions on visual system evolution for Laniidae and nocturnal owls that Renoult et al. ( J. Evol. Biol., 2009 ) study suggested may have flawed our early findings. Thus, the hypothesis that selection has resulted in increased detectability of nestling by adjusting gape coloration to parental visual systems is currently supported by our comparative data.     

Breeding success and predation on artificial nests of the endemic pigeons Bolle's Laurel Pigeon Columba bollii and White-tailed Laurel Pigeon Columba junoniae in the laurel forest of Tenerife (Canary Islands)

Breeding success and nest predation effects on the two Canarian endemic pigeons, Bolle's Laurel Pigeon Columba bollii and White-tailed Laurel Pigeon C. junoniae, were studied during 1995 in five zones of laurel forest on Tenerife Island. Nest predation was the more important cause of nesting failure of both species (88%), but principally affecting the White-tailed Laurel Pigeon. Experiments using artificial nests showed a greater predation on the ground than in trees and a lower predation in the February-March period than in June-July and September-October. The abundance of predators, estimated by bait consumption, showed a similar seasonal pattern, while fruit availability decreased over time from the first to third period. Predators identified by automatic cameras showed that Black Rat Rattus rattus was the major nest predator of both pigeons. These general patterns of nest predation affect the White-tailed Laurel Pigeon, which breeds on the ground mainly during April-July, much more than Bolle's Laurel Pigeon, which breeds in trees, especially in February-June. All seems to indicate that rats are the key factor causing the scarcity of the White-tailed Laurel Pigeon on Tenerife.