Offspring size-number trade-offs in scorpions: an empirical test of the van Noordwijk and de Jong model

Abstract Life-history traits are expected to exhibit negative phenotypic trade-offs, but often do not. In a seminal paper, van Noordwijk and de Jong (1986) provided an answer to this seeming paradox. According to their model, trade-offs will be more difficult to detect if variation in resource acquisition (or investment) is high relative to variation in resource allocation to the traits under consideration. Despite its influence on subsequent life-history studies, this model has rarely been tested. I use data from 10 species of scorpion (a total of 30 datasets, including multiple populations or years for some species) to test the van Noordwijk-de Jong model as modified to examine the relationship between offspring size and number. For both the overall data and a subset, including only the species Centruroides vittatus , I found that the correlation between offspring size and number within a population was significantly negatively correlated with the ratio of allocation variance to investment variance. That is, strong trade-offs were found when the investment variance was low relative to the allocation variance. These results were robust to the particular measure of offspring size and to whether offspring data were adjusted for female size variation. My results therefore provide strong evidence in support of the van Noordwijk and de Jong model.     

The size of cagA based on repeat sequence has the responsibility of the location of Helicobacter pylori in the gastric mucus and the degree of gastric mucosal inflammation

The aim of this study was to examine whether there is a relationship between cagA size of Japanese Helicobacter pylori strains and the location of these strains in the mucous layer, the degree of gastric inflammation and acid survival. Upper gastrointestinal endoscopies were done to 144 patients with dyspeptic symptom with informed consent, sera, biopsy specimens and H. pylori strains were obtained, and gastric histology and susceptibility to pH 3 of the strains were evaluated. To determine cagA size of Japanese strains using PCR, cagA of strain CPY3401 was sequenced. 74 H. pylori samples (72 cagA+) were obtained from the body and 56 samples (56 cagA +) obtained from the antrum. cagA size of 72 H. pylori strains from the body was mainly classified into 3 groups (short (48), middle (8), long (9), and others (7)) by PCR and all of that of 56 strains from the antrum except 2 was short. The size of cagA of isolated strains from the body is associated with enhanced gastritis, acid survival, and the location in the mucus. The long size cagA of which strain is acid sensitive, may be a strong selective pressure on strain that colonizes close to the host, which enhanced gastritis.     

Are mice calorically restricted in nature?

An important question about traditional caloric restriction (CR) experiments on laboratory mice is how food intake in the laboratory compares with that of wild mice in nature. Such knowledge would allow us to distinguish between two opposing views of the anti-aging effect of CR--whether CR represents, in laboratory animals, a return to a more normal level of food intake, compared with excess food consumption typical of laboratory conditions or whether CR represents restriction below that of animals living in nature, i.e. the conditions under which house mice evolved. To address this issue, we compared energy use of three mouse genotypes: (1) laboratory-selected mouse strains (= laboratory mice), (2) house mice that were four generations or fewer removed from the wild (= wild-derived mice) and (3) mice living in nature (= wild mice). We found, after correcting for body mass, that ad libitum fed laboratory mice eat no more than wild mice. In fact, under demanding natural conditions, wild mice eat even more than ad libitum fed laboratory mice. Laboratory mice do, however, eat more than wild-derived mice housed in similar captive conditions. Therefore, laboratory mice have been selected during the course of domestication for increased food intake compared with captive wild mice, but they are not particularly gluttonous compared with wild mice in nature. We conclude that CR experiments do in fact restrict energy consumption beyond that typically experienced by mice in nature. Therefore, the retarded aging observed with CR is not due to eliminating the detrimental effects of overeating.     

Estimation of the canopy-gap size using two photographs taken at different heights

A new, convenient method to estimate canopy-gap size using a camera is proposed. Canopy-gap size was estimated from two images taken with a vertically mounted, digital camera at high and low points (P_h and P_l) beneath a canopy gap. The actual (A_OBS) and estimated (A_1.0) canopy-gap sizes were highly correlated (R² > 0.93) for 16 canopy gaps in the Cryptomeria japonica D. Don. plantations, and the relationship between A_1.0 and A_OBS was expressed as A_1.0 = 1.16A_OBS. Thus, the method overestimated actual canopy-gap size by an average of 16%.     

Application of an image analysis system to the determination of biomass (ash free dry weight) of pond macroinvertebrates

The absence of a rapid and inexpensive method for estimating macroinvertebrate individual biomass is a limit to the study of freshwater communities, given that traditional methods are time- and money-consuming. We propose an inexpensive method to quickly estimate individual biomass from video-recorded images of pond macroinvertebrates. We used a software that automatically measures several body dimensions (area, perimeter, minor and major axes) on each individual and linear regression to relate these body dimensions to dry weight. Area was found to be the best predictor of dry weight. The method allows individual measures of macroinvertebrates at a reasonable speed and accuracy, and may be useful for biomass size spectra or secondary production studies.     

The effects of population size limitation on fecundity in mosaic populations of the clonal macrophyte Scirpus maritimus (Cyperaceae)

The clonal macrophyte Scirpus maritimus (Cyperaceae) propagates locally by rhizomes and reproduces sexually by achenes. The purpose of this paper was to examine whether in size-limited habitats in patchy and discrete marshes in two Mediterranean wetlands in southern France natural populations may suffer from a reduced maternal fecundity due to a deficit in outcross pollen. We first verified that S. maritimus suffers from a reduced fecundity when self-pollinated. At a site in the Camargue, mean fecundity (mean number of achenes per centimetre of spikelet) measured in 1995 and 1996 in seven and nine populations, respectively (surface area from 50 to 4500 m) increased significantly with population surface area in 1995 but not in 1996. In the second wetland at Roquehaute, which is composed of small ponds, fecundity was very low in all 12 local populations studied in 1996 (1.1 achenes per spikelet, SD = 1.2) and was not correlated with the population surface area (from 10 to 400 m). We performed a pollen supplementation experiment in five local populations at Roquehaute to determine whether this low fecundity may be due to a pollen limitation. A significant increase in fecundity after among-pond pollinations compared to within-pond pollinations indicated that local populations suffer from a deficit in outcross pollen, since each pond appears to contain one or a few number of clones (or incompatibility types). In S. maritimus, clonal spread may have a cost in terms of reduced fecundity in small habitats because each habitat is colonized by very few clones.     

A critical reappraisal of the fossil record of the bilaterian phyla

It has long been assumed that the extant bilaterian phyla generally have their origin in the Cambrian explosion, when they appear in an essentially modern form. Both these assumptions are questionable. A strict application of stem- and crown-group concepts to phyla shows that although the branching points of many clades may have occurred in the Early Cambrian or before, the appearance of the modern body plans was in most cases later: very few bilaterian phyla sensu stricto have demonstrable representatives in the earliest Cambrian. Given that the early branching points of major clades is an inevitable result of the geometry of clade diversification, the alleged phenomenon of phyla appearing early and remaining morphologically static is seen not to require particular explanation. Confusion in the definition of a phylum has thus led to attempts to explain (especially from a developmental perspective) a feature that is partly inevitable, partly illusory. We critically discuss models for Proterozoic diversification based on small body size, limited developmental capacity and poor preservation and cryptic habits, and show that the prospect of lineage diversification occurring early in the Proterozoic can be seen to be unlikely on grounds of both parsimony and functional morphology. Indeed, the combination of the body and trace fossil record demonstrates a progressive diversification through the end of the Proterozoic well into the Cambrian and beyond, a picture consistent with body plans being assembled during this time. Body-plan characters are likely to have been acquired monophyletically in the history of the bilaterians, and a model explaining the diversity in just one of them, the coelom, is presented. This analysis points to the requirement for a careful application of systematic methodology before explanations are sought for alleged patterns of constraint and flexibility.     

The Biology of the Nurse Shark,Ginglymostoma cirratum,Off the Florida East Coast and the Bahama Islands

The nurse shark is an extremely abundant shallow water species in Florida and the Caribbean, yet its biology is poorly known. Moreover, there is a great deal of misinformation about it in the literature. The maximum size and weight attained by the nurse shark have often been exaggerated. None of the specimens measured in this study exceeded 265cm TL and 114.5kg, and none of the specimens actually measured by other researchers exceeded 280cm. Females reach maturity at a length of 223–231cm, or at 86% of their maximum size. Males reach maturity between 214 and 214.6cm in length or at about 83% of their maximum size. Mating primarily occurs from mid-June to early July. The embryos are enclosed in sturdy egg capsules for the first 12–14 weeks of gestation. In a gravid female, the embryos are at different stages of development during the first four months of gestation. Embryos are lecithotrophic and there is no evidence of any supplemental mode of embryonic nourishment. Embryos measure 28–30.5cm at birth. The gestation period is estimated at about five to six months. Brood sizes are large, ranging from 21 to 50 young, with a median of 34 young. The reproductive cycle of the nurse shark consists of a five to six-month gestation period and a two-year ovarian cycle. Thus, the reproductive cycle is biennial and a female produces a brood every two years. The nurse shark is an opportunistic predator that consumes a wide range of small fishes, primarily grunts (Haemulidae).     

On power and sample size calculations for likelihood ratio tests in generalized linear models

A direct extension of the approach described in Self, Mauritsen, and Ohara (1992, Biometrics 48, 31-39) for power and sample size calculations in generalized linear models is presented. The major feature of the proposed approach is that the modification accommodates both a finite and an infinite number of covariate configurations. Furthermore, for the approximation of the noncentrality of the noncentral chi-square distribution for the likelihood ratio statistic, a simplification is provided that not only reduces substantial computation but also maintains the accuracy. Simulation studies are conducted to assess the accuracy for various model configurations and covariate distributions.     

Competitive ability and the coexistence of anuran larvae in freshwater rock‐pools

• 1 I examined the competitive ability of larval common frogs (Rana temporaria) and common toads (Bufo bufo) in a laboratory experiment by manipulating the number and size of Rana and the number of Bufo.
• 2 Bufo was the most active tadpole type, whereas small Rana was more active than large Rana.
• 3 Especially at high food availability, the growth rate of large Rana at metamorphosis was reduced in the presence of small Rana, whereas that of small Rana was not affected by larger conspecifics.
• 4 Both size classes of Rana were negatively affected by the presence of Bufo. Size at metamorphosis of Bufo was greater when large Rana was present. These results suggest that activity level is important in determining competitive ability.
• 5 To study competition in the field, tadpoles of Bufo were introduced to small rock‐pools that did not support Bufo naturally, but were with or without Rana.
• 6 In the experimental pools, there were no interspecific effects on the growth rate of either species. However, the growth rate of Bufo was lower in the experimental pools than in pools inhabited naturally. Futher, survival of Bufo was low in small pools. Lower food availability or physical factors associated with small pools, rather than interspecific competition, may be the reason why Bufo avoids breeding in small rock‐pools.