Nutrient transfer functions: the site of integration between feeding behaviour and nutritional physiology

Summary. We describe and extend a graphical approach to quantitative nutrition that focuses on the interplay between behavioural and physiological components of nutritional regulation. The site of integration is the nutrient transfer function, which is the function describing the time course of nutrient transfer between serially connected nutritional compartments (e.g., from the gut to the blood). The relationship between the shape of the nutrient transfer function and the temporal patterns of feeding determines the values of two key quantitative parameters of nutrition: the rate ('power') and the efficiency of nutrient acquisition. The approach can be extended to consider, in addition to the short-term behavioural and physiological decisions made by animals, some ecological determinants and longer-term, life history consequences of such decisions. Most importantly, this category of models can provide insights into the interplay among the various nutrients in an animal's diet. We illustrate this using hypothetical examples, and also present preliminary data for the power-efficiency relationships of protein and digestible carbohydrates in locusts. Finally, we consider existing evidence for the various means available to these and other insects for regulating such relationships. Received 24 September 1997; accepted 9 December 1997.     

Evolution of reproductive features and larval development in the genus Amphiglena (Polychaeta: Sabellidae)

Larval development in Amphiglena mediterranea is direct in the parental tube, and larvae crawl away as young juveniles with a radiolar crown capable of feeding. The non-feeding larvae of A. nathae are initially brooded in the parental tube, and then have a swimming phase before settling and developing a radiolar crown. Developmental data and reproductive features such as sperm structure are combined with other morphological data for an assessment of the cladistic relationships of the species in the genus Amphiglena. Two species of Laonome are included as part of the ingroup. Six genera, representing a sister group to the Laonome/Amphiglena clade, are used as an outgroup. Two most-parsimonious cladograms were found, and the evolution of reproductive features are discussed. The monophyly of Amphiglena is indicated by features previously identified, as well as two features based on sperm morphology. At present a plesiomorphic larval form cannot be identified for the genus Amphiglena. Received: 16 June 1997 / Accepted: 29 January 1998     

Parentage and sex allocation in the facultatively polygynous ant Myrmicatahoensis

Most social groups have the potential for reproductive conflict among group members. Within insect societies, reproduction can be divided among multiple fertile individuals, leading to potential conflicts between these individuals over the parentage of sexual offspring. Colonies of the facultatively polygynous ant Myrmicatahoensis contain from one to several mated queens. In this species, female sexuals were produced almost exclusively by one queen. The parentage of male sexuals was more complex. In accordance with predictions based on worker sex-allocation preferences, male-producing colonies tended to have low levels of genetic relatedness (i.e., high queen numbers). Correspondingly, males were often reared from the eggs of two or more queens in the nest. Further, over half of the males produced appeared to be the progeny of fertile workers, not of queens. Overall investment ratios were substantially more male biased than those predicted by genetic relatedness, suggesting hidden costs associated with the production of female sexuals. These costs are likely to include local resource competition among females, most notably when these individuals are adopted by their maternal nest. Received: 3 March 1998 / Accepted after revision: 20 June 1998     

Queen control of egg fertilization in the honey bee

The study investigated the precision with which honey bee queens can control the fertilization of the eggs they lay. Because males and workers are reared in different-sized cells, the honey bee is one of the few Hymenoptera in which it is possible for the experimenter to know which type of egg a queen “intends” to lay. Eggs were collected from both worker and drone (male) cells from four honey bee colonies. Ploidy of the embryo was determined using polymorphic DNA microsatellites. All 169 eggs taken from worker cells were heterozygous at at least one microsatellite locus showing that the egg was fertilized. All 129 eggs taken from drone cells gave a single band at the B124 locus, strongly suggesting haploidy. These data show that honey bee queens have great, and quite possibly complete, ability to control the fertilization of the eggs they lay. Data from the literature suggest that in two species of parasitoid Hymenoptera (Copidosoma floridanum, Colpoclypeus florus) females have great, but not complete, ability to control fertilization. Received: 23 December 1997 / Accepted after revision: 17 May 1998     

Genetic divergence and phylogenetic inferences in five species of Mugilidae (Pisces: Perciformes)

Allozyme electrophoresis was used to compare the genetic divergence of global populations of Mugil cephalus Linnaeus, 1758 and two congeneric [M.␣curema Cuvier & Valenciennes, 1836; M. gyrans (Jordan & Gilbert, 1885)] and two more distantly related [Liza ramada (Risso, 1826); Xenomugil thoburni (Jordan & Starks, 1896)] species on the basis of 18 enzyme loci. The amount of genetic divergence among the species examined is in agreement with their present systematic status, the differences being larger among non-congeneric species than among species of the same genus. Intraspecific genetic distances in M. cephalus (average Nei's D= 0.154), although higher than those reported for conspecific populations of fish, appear to be small when compared to the interspecific values among mugilid species (0.821 ≤ Nei's D ≤ 1.744). Phylogenetic trees obtained by genetic distance methods and discrete character parsimony analysis were of similar topology, except for the relationships within the genus Mugil and for the arrangement of M. cephalus populations. Received: 7 April 1997 / Accepted: 4 February 1998     

A Preliminary Study of Geographic Influence on Arsenic Concentrations in Human Hair

Past mining activities in the county of Cornwall in the United Kingdom, has exposed the local environment to raised levels of As. Previous research has shown an increased concentration of As in crops grown in such areas and the subsequent take-up of As through the food chain may lead to an increased body burden in man. In an attempt to evaluate this, a pilot study was carried out using Particle Induced X-ray Emission to compare the hair As concentration of a group of Cornish residents to that of a control group consisting of residents in the counties of Oxfordshire and Wiltshire. The null hypothesis being that there is no significant difference between the hair As concentrations of the two groups.Each group comprised thirty six age and sex matched subjects. The mean hair As concentration for the Cornish group was 2.51 g g-1, which is significantly greater than that of 0.7 g g-1 found in the control group (p = 0.004). The World Health Organisation suggests a hair As value greater than 1 g g-1 as evidence of increased exposure to As and 5 g g-1 is quoted by the Canadian Government as evidence of significant ingestion of As. Twenty one Cornish subjects registered a value at or above 1 g As g-1 compared to nine in the control group (p = 0.0003). Five subjects in the Cornish group had values that exceed 5 g As g-1, compared to only two in the control group (p = 0.23). We use the results of this study as evidence to support our continued work in this area in order to evaluate possible health implications.     

Seasonality of polypide recycling and sexual reproduction in some erect Antarctic bryozoans

The seasonality of polypide cycling has been investigated for three species of erect bryozoans from Antarctica: Isoseculiflustra rubefacta (Kluge, 1914), Nematoflustra flagellata (Waters, 1904) and Himantozoum antarcticum (Calvet, 1905). Approximately ten colonies of each species were collected monthly by SCUBA divers over a 14 mo period during 1992/1993, and the status of each individual zooid was classified as differentiating/regenerating, active (feeding autozooids), degenerate (brown body) or sexually reproductive (ovicells present, or zooid containing a larva). Polypide cycling in all three species was distinctly seasonal. New zooids formed at the growth margin and typically contained actively feeding polypides for ≃9 mo before these polypides degenerated into brown bodies in the austral winter (June). Very few polypides were active in the period from June to August, when water-column food levels were at their lowest; after this period new polypides differentiated. Individual zooids typically underwent a total of five (I. rubefacta and N. flagellata), or at least four (H. antarcticum) complete polypide cycles before becoming senescent. Polypide lifetimes generally became shorter as the age of the zooid increased. Sexual reproduction was also distinctly seasonal in these species, with bands of ovicells or sexually reproductive zooids being formed each year in late summer once a given colony had grown to a threshold size (or age). Larvae were then brooded for ≃10 mo before being released in January/February (N. flagellata) or February/March (H. antarcticum). The seasonal patterns of polypide cycling are related clearly to the variations in food availability, and these species appear to have the longest zooid lifetime (≃5 yr) and the slowest polypide cycling (once per year with polypide lifetimes up to 10 mo) reported for any bryozoan so far. Received: 7 May 1995 / Accepted: 19 November 1997     

Monopolization in a resource queue: water striders competing for food and mates

The monopolization of resources plays an important theoretical role in the literature on competition for food and mates. We used 12 groups of male water striders (Aquariusremigis) to: (1) test the general prediction that monopolization of both food and mates decreases as the temporal clumping of resources increases, (2) compare the efficiency of two indices of resource monopolization, coefficient of variation and Q (Ruzzante et al. 1996), and (3) quantitatively assess the resource queue model of Blanckenhorn and Caraco (1992). Each group of six males competed for both food items and mates released from the upstream end of a laboratory stream. The mean inter-arrival time for resource units (food or females) was 10 min, with four levels of temporal clumping (variance in inter-arrival time: 0, 25, 50 or 320 min²). As predicted, the monopolization of both food and mates decreased as the temporal clumping of resource arrival increased, although monopolization was greater for food than for mates. Q detected the difference in monopolization of food and mates, whereas the coefficient of variation did not, because Q is independent of mean resource abundance. The resource queue model successfully predicted monopolization of both resource types, explaining 89% and 76% of variation in the proportion of food and mates acquired by the six males. The success of the model suggests that the scaling of handling time to the variance in resource inter-arrival time should play an important role in any general theory of resource monopolization. Received: 28 February 1997 / Accepted after revision: 26 September 1997     

Uptake of arsenate, trimethylarsine oxide, and arsenobetaine by the shrimp Crangon crangon

Common shrimp, Crangon crangon (L.), were exposed to inorganic arsenic (arsenate), trimethylarsine oxide, or arsenobetaine in sea water (100 μg As l⁻¹) or in food (1 mg As g⁻¹ wet wt) for up to 24 d, followed by 16 d depuration in clean sea water with undosed food, in order to determine the efficiency of uptake and retention of the compounds. Accumulation of arsenic in the tail muscle, gills, midgut gland, exoskeleton, and remaining tissues was found to depend on the chemical form of the arsenic and the route of exposure. No arsenic was accumulated by C. crangon exposed to arsenate or trimethylarsine oxide in sea water. Shrimps exposed to waterborne arsenobetaine initially accumulated a small amount of arsenic in their tail muscle and gills. After 16 d, C. crangon fed arsenate, trimethylarsine oxide, or arsenobetaine had accumulated arsenic in their tail muscle to levels ∼2-, 2-, or 40-times, respectively, that of the control group. A roughly linear rate of accumulation was shown by shrimps fed trimethylarsine oxide or arsenobetaine, but C. crangon fed arsenate accumulated arsenic for 16 d, then lost arsenic such that their concentration on Day 24 was not significantly different from that of the control group. Patterns of arsenic accumulation in the gills of shrimps fed the compounds were similar to those seen in the tail muscle. On a whole animal basis, C. crangon retained ∼1.2% of the arsenate, 1.6% of the trimethylarsine oxide, and 42% of the arsenobetaine consumed over the first 16 d of exposure, with roughly half present in the tail muscle in each case. Data obtained support the view that the direct uptake of arsenobetaine from sea water does not make a significant contribution to the relatively high concentrations of this compound in marine crustaceans, and that food is the primary source. Naturally occurring arsenic compounds in C. crangon and possible transformations of the administered arsenic compounds were examined by high performance liquid chromatography using an inductively coupled plasma mass spectrometer as the arsenic-specific detector. Control C. crangon contained arsenobetaine as the major arsenic compound (>95% of total arsenic); tetramethylarsonium ion (0.7%) and an unknown arsenic compound (1.7%) were also present as minor constituents. Shrimp ingesting arsenobetaine accumulated it unchanged. Shrimp ingesting arsenate did not form methylated arsenic compounds; they appeared to contain their accumulated arsenic as unchanged arsenate only, although the possibility that some of the arsenic was reduced to arsenite could not be excluded. C. crangon ingesting trimethylarsine oxide biotransformed the compound predominantly to dimethylarsinate. Received: 9 October 1997 / Accepted: 11 February 1998     

Production of tropical copepods in Kingston Harbour, Jamaica: the importance of small species

The copepod community observed during an 18-month period at the mouth of eutrophic Kingston Harbour, Jamaica, was dominated by small species of Parvocalanus, Temora, Oithona, and Corycaeus. Mean copepod biomass was 22.1 mg AFDW m⁻³ (331 mg m⁻²). Annual production was 1679 kJ m⁻², partitioned as 174 kJ m⁻² naupliar, 936 kJ m⁻² copepodite, 475 kJ m⁻² egg and 93 kJ m⁻² exuvial production. All nauplii, most copepodites and many adults, equivalent to half of the biomass and production, were missed by a standard 200-μm plankton net, emphasizing the importance of nauplii and small species in secondary production estimates. The evidence suggests that growth rates and production are generally not food limited, and we speculate that size-selective predation shapes the structure of the harbour community. Biomass and production are higher than previous estimates for tropical coastal waters, but comparable to other eutrophic tropical embayments and many productive temperate ecosystems. Far from being regions of low productivity, tropical zooplankton communities may have significant production and deserve greater research attention than they currently receive. Received: 19 September 1997 / Accepted: 21 October 1997