Clutch size manipulation, hatching success and offspring phenotype in the ball python (Python regius)

In a diverse array of avian and mammalian species, experimental manipulations of clutch size have tested the hypothesis that natural selection should adjust numbers of neonates produced so as to maximize the number of viable offspring at the end of the period of parental care. Reptiles have not been studied in this respect, probably because they rarely display parental care. However, females of all python species brood their eggs until hatching, but they do not care for their neonates. This feature provides a straightforward way to experimentally increase or reduce clutch size to see whether the mean clutch size observed in nature does indeed maximize hatching success and/or optimize offspring phenotypes. Eggs were removed or added to newly laid clutches of Ball Pythons ( Python regius ) in tropical Africa (nine control clutches, eight with 50% more eggs added, six with 42% of eggs removed). All clutches were brooded by females throughout the 2-month incubation period. Experimental manipulation of clutch-size did not significantly affect the phenotypes (morphology, locomotor ability) of hatchlings, but eggs in 'enlarged' clutches hatched later, and embryos were more likely to die before hatching. This mortality was due to desiccation of the eggs, with females being unable to cover 'enlarged' clutches sufficiently to retard water loss. Our results support the notion of an optimal clutch size, driven by limitations on parental ability to care for the offspring. However, the proximate mechanisms that generate this optimum value differ from those previously described in other kinds of animals. © 2003 The Linnean Society of London . Biological Journal of the Linnean Society 2003, 78 , 263–272.     

Thirsty sea snakes forsake refuge during rainfall

Abstract Vertebrates living in dry or salty habitats spend significant amounts of time and energy maintaining their hydro‐mineral balance; any opportunity to drink fresh water should reduce such expenses. However, to find fresh water, individuals are generally forced to leave the safe and buffered conditions that prevail in their refuges. Therefore, they must face harsh environmental conditions and increased predation risks. We examined this trade‐off in the field, using a very large dataset gathered on amphibious sea snakes that confront periodic droughts. The study was carried out on different islets in the lagoon of New Caledonia. As expected, sea kraits remain concealed most of the time under rocks or within burrows during dry weather. They select precise time windows to move rapidly between the sea and the land, thereby minimizing the time spent in the open. Rainfall triggered massive disruptions of this rhythm: many snakes quickly forsook their shelter to drink in the open, and remained almost motionless until satiety. Interestingly, they adopted specific and unusual postures to drink. They perched on the top of rocks that were benefiting from running and less salty water during downpours. They also drank the droplets attached to vegetation during drizzle.     

A cyanobacterial bloom prevents fish trophic cascades

1. We experimentally compared the impacts of visually feeding zooplanktivorous fish and filter‐feeding omnivorous fish in shallow tropical Dakar Bango reservoir, Senegal. We provoked a cyanobacterial Anabaena bloom under mesotrophic to eutrophic N‐limited conditions in 18 enclosures assigned to six Nile tilapia life‐stage treatments, at typical biomasses: fishless control (C), zooplanktivorous fry (Z), omnivorous juveniles (O), herbivorous fingerlings (H) and two combinations (OZ, OH). 2. All fish grew well, but as prevalent inedible phytoplankton dampened fish effects, community‐level trophic cascades did not occur. Planktivore types acted independently and affected differentially the biomasses of total zooplankton, cyclopoids, nauplii, cladocerans, invertebrate carnivores, large herbivores, colonial cyanobacteria and Chlorophyta. They neither influenced the total biomass of phytoplankton, nor most water chemistry characteristics. Responses were apparently not fish‐biomass related. The bloom collapsed synchronously in all enclosures, coinciding with enrichment ending, with a return to clear water within 12 days. 3. Our results support the hypothesis that excess nutrients and prevalent inedible cyanobacteria inhibit the cascading effects of natural biomass levels of both visually feeding zooplanktivores and filter‐feeding omnivores. In N‐limited meso‐eutrophic shallow tropical lakes with predominantly small herbivorous zooplankton, neither the type nor the biomass of planktivorous fish present seems likely to prevent the transient outburst of cyanobacterial blooms. Such fragile ecosystems may thus not sustain a trophic state suitable for drinking water production, unless human impacts are restricted. The generality of restoration approaches based on ecological engineering should be further explored.     

A new Coryphoid palm genus from Madagascar

Tahina J.Dransf. & Rakotoarinivo, gen. nov. (Arecaceae) is described as a new genus from north-western Madagascar, with a single species T. spectabilis J.Dransf. & Rakotoarinivo, sp. nov. Tahina is included within tribe Chuniophoeniceae of subfamily Coryphoideae, based on the strictly tubular imbricate rachilla bracts, the flowers grouped in cincinni with tubular bracteoles, and the stalk-like base to the corolla. This position is corroborated by evidence from plastid DNA. Lamina anatomy is discussed in detail, and similarities with and differences from the other members of Chuniophoeniceae are discussed. Based on the ecological characteristics of the single locality, predictions are made on where else it may occur in Madagascar.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 79–91.     

Phylogenetic relationships of a new genus and species of microteiid lizard from the Atlantic forest of north-eastern Brazil (Squamata, Gymnophthalmidae)

A new genus and species of a short limbed and slightly elongate gymnophthalmid lizard is described from the Atlantic rain forests of north-eastern Brazil. The new genus is also characterized by short and stout pentadactyl limbs, presence of prefrontals, absence of frontoparietals, distinctive ear opening and eyelid, two pairs of genials, a distinct collar, smooth, quadrangular, dorsal scales, quadrangular ventrals, fused postfrontal and postorbital bones, and two pairs of sternal ribs. The geographical distribution of the new taxon extends from the state of Rio Grande do Norte to the northern bank of the Rio São Francisco in the state of Alagoas. All specimens were obtained in leaf litter, an observation which agrees with the fossorial habits suggested by the body shape and massive aspect of the head of this species. A phylogenetic analysis based on external morphology, osteology, and molecular data recovered the new lizard as the sister genus to Anotosaura , and Colobosauroides as the sister group to these two.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 144 , 543−557.     

Effect of different soil and clove treatments in the control of white rot of garlic

Soil solarisation was consistently efficacious in reducing inoculum density to undetectable levels in a field naturally‐infested with Sclerotium cepivorum. This treatment delayed epidemic onset of white rot of garlic 2–3 months as compared with the untreated control or the inoculation of planting furrows with Glomus intraradices. Furthermore, significant reductions of disease incidence and of the standardised AUDPC were also observed in solarised plots, resulting in quantitative and qualitative yield improvement. Similar effects were observed in plots planted with tebuconazole‐treated cloves, confirming previous results, whereas Trichoderma harzianum was ineffective as a biocontrol agent, when applied to planting furrows. The inoculation of plots with G. intraradices before planting, in three consecutive years, was neither effective for disease control nor on the development of garlic, although the root systems of garlic plants from all the experimental treatments were heavily mycorrhizal at harvest, indicating the presence of native arbuscular mycorrhizal propagules in the soil and their survival after soil solarisation.     

Metapopulation genetic structure in the water vole, Arvicola terrestris, in NE Scotland

The genetic structure of nine colonies of the water vole, Arvicola terrestris , in one area of NE Scotland was studied. Non-destructive samples from 478 individuals (mostly immature animals) were typed for 12 microsatellites. Cases of Hardy-Weinberg disequilibrium were frequent within all colonies. The five colonies in the inland part of the study area also showed frequent cases of linkage disequilibrium. All colonies showed high levels of genetic diversity (unbiased H = 0.52-0.74). All five colonies sampled in successive years showed significant annual changes in genetic composition. All colonies showed genetic differentiation from each other, whether measured by average 6, pairwise 9 or pairwise Nei's genetic distance. The spatial pattern of genetic differentiation was consistent with either a stepping-stone model over the whole study area or an island model within the coastal and inland parts and an intervening barrier to gene flow. The study suggested that the genetic structure of colonies of A. terrestris often departs from the equilibrium states assumed by traditional mefhods for the study of gene flow, and that a parentage-based approach would be fruitful.     

Body size variation in Audouin's Gull Larus audouinii; a density-dependent effect?

A significant decrease in the body size of Audouin's Gulls Larus audouinii breeding at the Chafarinas Islands is reported. The decrease in linear measurements in the current breeding population ranged from 2.5% to 5.6% in males and from 0.61% to 4.4% in females. This was detected when assessing the reliability of a sex-discriminating function derived for the same colony 13 years earlier. When applied to the current population, this function failed to predict the sex of a large proportion of males (44%). The relative decrease in mean size was significantly greater in males than in females for culmen, nalospi and tarsus lengths, while for bill depth at culmen, wing length and body mass the relative decrease was similar in both sexes. Since the extent of differences depended on sex, these differences cannot be attributed to a systematic between-observer bias. Mean body size reduction might be either the result of a greater proportion of small breeding birds in the current population, because of increased availability of nesting sites (competition relaxation hypothesis), or an outcome of environmental factors affecting growth parameters (environmental constraint hypothesis). According to the first hypothesis, the changes observed would be associated with higher variability values. Conversely, if the second is true, the degree of variability should be similar. Since there are no significant differences in the degree of variability shown in the two data sets, our results support the second hypothesis. The environmental constraint acting via growth parameters is probably related to the increase in the number of Audouin's Gull breeding pairs while food availability was depleted. Our data suggest that changes in the duration of the growth period, rather than in the growth rates themselves, are involved in the body size differences found.     

Calcium in Xylem Sap and the Regulation of its Delivery to the Shoot

Amounts of total and free calcium in root and shoot xylem sapwere quantified for a number of species grown in comparableenvironments and in a rooting medium not deficient in calcium.The potential for the shoot to sequester calcium was also examined,along with the ability for ABA to regulate calcium flux to theleaf. Xylem sap calcium showed considerable interspecific and diurnalvariation, even though the plants were grown with similar rhizosphericcalcium concentrations. The potential for the shoot to sequesterxylem sap calcium was also highly variable between species andimplied an ability, at least in some species, to regulate thecalcium reaching the shoot in the transpiration stream. Long distance transport of calcium in the xylem was not primarilyby mass flow, because neither calcium uptake nor distributionwere closely related to water uptake or transpiration. The diurnalchanges in xylem sap total ion concentration appeared to benegatively correlated with transpiration while, in contrast,the calcium ion concentration showed two peaks, one occurringin the dark and the other in the light period. The application of ABA to roots caused an increase in the rateof exudation from the xylem of detopped well-watered plants.These experiments suggest that changes in root water relationsdriven by ionic fluxes were the likely cause for enhanced sapexudation from ABA-treated roots. The steady-state concentrationof calcium in the xylem sap was unaffected by ABA when exudationrate increased and, consequently, the flux of calcium must alsohave increased. Key words: Abscisic acid, calcium, xylem sap, ionic fluxes