The effects of landscape-level disturbance on the composition of Minnesota caddisfly (Insecta: Trichoptera) trophic functional groups: evidence for ecosystem homogenization

Over 300,000 caddisfly specimens representing 249 species were collected from nearly 250 sites throughout Minnesota during 2000 and 2001 to determine the effects of human disturbance on the composition of caddisfly trophic functional groups at the landscape level. Canonical correspondence analysis determined that stream width was the most important variable influencing functional group composition in regions of the state with relatively low disturbance, and that differences in the caddisfly fauna between sizes of streams generally followed trends predicted by the river continuum concept. In regions of the state with moderate disturbance, both stream width and the percentage of disturbed habitat upstream of a site were important variables influencing functional group composition. In highly disturbed regions, no variables corresponded to changes in the composition of caddisfly functional groups. Instead, ecosystems were homogeneous: fine-particle filtering collectors dominated in all sizes of streams. The observed aquatic ecosystem homogenization is attributed mostly to input of fine-particle organic and inorganic sediment from extensive agriculture.     

Preparation and evaluation of candidate certified reference materials (CRMs) for nutrients in seawater

Certified reference materials (CRMs) are an essential part of the quality assurance (QA) necessary for the reliable analytical measurement of nutrients in seawater. The CRMs currently available for these analyses are not matrix matched to marine samples. QUASIMEME routinely produces test materials for the nutrients in seawater and nutrients in estuarine water and low-salinity open water Laboratory Performance Studies (LPS) that are both homogeneous and stable. QUASIMEME, in conjunction with Eurofins Scientific, Denmark have produced two reference materials (RMs). The homogeneity testing and preliminary stability studies were carried out by QUASIMEME, and the results are presented in this article. Participants of the QUASIMEME LPS who demonstrated satisfactory long-term performance for the analysis of nutrients in seawater and nutrients in estuarine water and low-salinity open water were invited to take part in the certification exercise. Twenty laboratories returned data, a summary of which is also presented. The certification and long-term stability testing and additional data analysis were carried out by Eurofins Scientific, Denmark, and are outwith the scope of this article and not reported here. Eurofins Scientific, Denmark have marketed these RMs as part of their range of VKI Reference Materials (further information is available from eurofins@eurofins.dk).     

Poisoned plusiines: toxicity of milkweed latex and cardenolides to some generalist caterpillars

Summary. Larvae of Trichoplusia ni Hübner (Lepidoptera: Noctuidae) that ingested latex from Asclepias curassavica L. (Asclepiadaceae) often regurgitated and convulsed with spasms before becoming immobile and unresponsive. Some larvae required over a day to recover sufficiently to feed. Latices from four other plant species in three families were all deterrent, but none caused detectable poisoning. The toxicity of A. curassavica latex was evidently due to cardenolides because pure cardenolides had similar effects when ingested by T. ni. Other species of noctuid caterpillars (Rachiplusia ou Guenée, Anagrapha falcifera Kirby, and Autographa precationis Guenée) sometimes also suffered spasms and temporary immobility when fed A. curassavica latex. A more distantly related noctuid, Spodoptera ornithogalli, was deterred by the latex, but showed no overt physiological responses at the dosage tested. T. ni larvae failed to develop on intact leaves of A. curassavica, on leaves with latex canals deactivated by midrib severance, and on excised leaves. Similarly, larvae reared on excised A. syriaca L. leaves to the final instar died when transferred to A. curassavica leaves with either intact or severed midribs. The final instar larvae sometimes suffered from spasms and immobility even when confined on leaves with depressurized canal systems. Evidently, cardenolides stored outside the latex system suffice to poison larvae. We conclude that cardenolides in A. curassavica have potent physiological effects on some generalist caterpillars and that the presence of these compounds both inside and outside laticifers effectively protects the plant. Received 30 June 1999; accepted 18 October 1999     

Phylogeny and biogeographic history of hake (genus Merluccius), inferred from mitochondrial DNA control-region sequences

 Phylogenetic analyses of the left domain of the mitochondrial DNA control-region sequence have been used to examine the relationships among species of the genus Merluccius (Rafinesque, 1810), and to compare these with hypotheses based on morphological, meristic and allozyme characters. Analysis of aligned sequences revealed that transition bias was much lower than in mammalian mtDNA, and that nucleotide composition of control-region sequences was biased toward A and T. We have roughly calibrated a molecular clock for the genus, based on the rise of the Isthmus of Panamá, which is believed to have created a barrier to dispersal between marine species of the Atlantic and Pacific Oceans. Our mtDNA-based phylogeny was highly congruent with allozyme-based phylogenies, but poorly so with a previously described phylogeny based on morphology. Specifically, our phylogeny resolved two well-supported principal clades, one of American (west Atlantic and east Pacific) species and the other of Euro–African (east Atlantic) species. This suggests an evolutionary history during which the ancestral lineage of Merluccius was divided between two geographic regions, with subsequent dispersal and vicariant events resulting in the evolution and distribution of extant taxa. However, the relationships between some taxa within the American clade could not be resolved. We suggest that this is consistent with an hypothesis of a rapid origin and radiation of these taxa. Received: 12 December 1998 / Accepted: 15 October 1999     

Short retention times of stomach temperature loggers in free-living seabirds: is there hope in the spring?

Stomach temperature loggers have proved useful for the study of feeding activity in free-living seabirds, but their usage has been restricted because they are frequently dislodged and lost during the seabirds' regular regurgitation of indigestible prey remains. In the present study we examine the incidence of spontaneous regurgitation (pellet production) in free-living seabirds, consider the effect this has on the likely retrieval of stomach temperature loggers and present a structural modification of the logger housings which leads to a much lower incidence of regurgitation. Systems were tested on albatrosses, cormorants, gannets and penguins. Received: 15 July 1997 / Accepted: 31 October 1997     

Coalitionary mate guarding by male chimpanzees at Ngogo, Kibale National Park, Uganda

Cooperative mate guarding by males is unusual in mammals and birds, largely because fertilizations are non-shareable. Chimpanzees live in fission-fusion communities that have cores of philopatric males who cooperate in inter-group aggression and in defending access to the females in their community. Male contest mating competition is restrained within communities, but single high-ranking males sometimes try to mate guard estrous females. Data from an unusually large chimpanzee commmunity at Ngogo, Kibale National Park, Uganda, that contains more males than any previously studied community show new variation in chimpanzee mate-guarding behavior. Contrary to expectation given the large number of males, mate guarding was as common as, or more common than, at other sites, and males other than the alpha male guarded more often. More strikingly, pairs or trios of top-ranking males sometimes engaged in cooperative aggression to prevent estrous females from mating with other males, but tolerated each other's mating activities. Both single males and coalitions mostly guarded periovulatory females. Mate-guarding coalitions were previously unknown in chimpanzees. Coalitions occurred in large mating parties, seemingly because these often contained too many males for single males to maintain exclusive access to estrous females. Coalition members gained higher shares of copulations than they could have expected from solo mate guarding, and suffered lower per capita costs of guarding (as inferred from aggression rates). Two males who most often participated in coalitions formed two-male coalitions at about the point where the number of males present made it unlikely that either could get 50% or more of total copulations on his own, and formed trios when this value dropped below 33%. Kin selection could be a factor in cooperation among male chimpanzees, but coalition members were not necessarily close relatives and the apparent structure of payoffs fit that of mutualism. Furthermore, reliance of male chimpanzees on support from allies to maintain high rank could have led to trading of mating exclusivity for support against mating competitors. Received: 28 May 1997 / Accepted after revision: 16 May 1998     

Spawning behaviour and sex hormone levels in adult and precocious brown trout (Salmo trutta L.) males and the effect of anosmia

Summary. In the present experiment the behaviour and endocrine status of males of the brown trout, Salmo trutta L., (Salmoniformes: Salmonidae) were studied when males were kept in a stream tank with a nest digging female. Groups of mature adult males and precocious intact or anosmic male parr were placed with the nesting female so that the group resembled a natural spawning situation with big anadromous fish acting as dominant males and precocious parr acting as “sneakers”. A control experiment was also run with only males without a female present. In intact parr there were significant positive correlations between the per cent of the total observation time spent with a female, milt volume, and plasma concentration of 17α, 20β-dihydroxy-4-pregnen-3-one. Anosmic parr had significantly lower volumes of strippable milt and gonadal steroid hormone levels compared with intact parr. However, no differences were found in the control experiment. Significantly fewer anosmic parr attended and courted the nesting female and those anosmic fish that attended the female had significantly lower plasma levels of gonadal hormones. Intact parr also displayed a greater number of agonistic acts against other parr without any difference in fighting ability. No differences in aggression occured in the control experiment. In adult males together with a female, post-experimental gonadal steroid hormone levels were higher than pre-experimental levels. Positive correlations between aggression and androgen hormone levels were observed in adult males. No differences in plasma hormone levels were observed between adult males and intact precocious males. The results show that olfactory occlusion results in low steroid hormone levels and milt volumes in precocious males placed in a spawning situation. The courting behaviour was also affected by anosmia. Odours from the nesting female may have caused the enhanced plasma hormone levels and stimulated the males to attend the female. Received 15 May 1997; accepted 29 June 1997.