Impact of Hybridization on a Threatened Trout of the Southwestern United States

Trouts native to the American Southwest provide an excellent example of the plight of endangered fishes from this region. The native species, Apache trout and Gila trout ( Oncorhynchus apache and O. gilae , respectively) have faced drastic reduction in habitat and detrimental interactions with introduced species, resulting in a dramatic decrease in numbers and sizes of populations. We used biochemical methods to identify diagnostic markers for the estimation of genetic relatedness and analysis of hybridization among native trouts and introduced cutthroat and rainbow trouts ( O. clarki and O. mykiss , respectively). Restriction endonuclease analysis of mitochondrial DNA (mtDNA) indicated that Apache and Gila trout were very similar to each other, and more similar to rainbow trout than cutthroat. Diagnostic allozyme marker loci indicated that Apache trout hybridized extensively with rainbows in four populations and provided no evidence for reproductive isolation between the forms. Analysis of mtDNA, however, indicated that introduced haplotypes were rare in these same individuals, identifying a bias in the direction of gene exchange between species. The potential reproductive isolation and lack of information concerning population structure necessitate further study of Apache trout to determine the appropriate management strategy for this threatened species. This case demonstrates that extreme care must be exercised when considering elimination of any contaminated population lest the unique genetic identity of the native taxon be lost forever.     

Developmental change in aggregation,defense and escape behavior of buckmoth caterpillars,Hemileuca lucina (Saturniidae)

Summary Changes in response to attack and the tendency to aggregate were examined in the six larval instars of the buckmoth, Hemileuca lucina (Saturniidae). In response to simulation of attack by a parasitoid and of biting by a predator, early instars (I, II, and III) exhibited defensive behavior much more often than escape behaviors, whereas late instar larvae (IV, V, and VI) usually resorted to escape rather than defend themselves. The situations in which attacked larvae were most likely to stimulate other group members to respond were: second and third instar larvae thrashing in response to simulation of a parasitoid or headrearing in response to simulation of a biting predator; and fourth, fifth and sixth instar larvae dropping in response to either stimulus. An index of reaggregation indicated that first instar larvae had difficulty reaggregating; second, third and fourth instar larvae reaggregated quickly; and fifth and sixth larvae dispersed. As larvae developed, the change from predominantly defense to escape behaviors paralleled the decline in tendency to aggregate.     

Phenotype interactions in group behavior of honey bee workers (Apis mellifera L.)

Summary The alarm reaction of groups of honey bee workers was quantified using a metabolic bioassay. The genetic structure of these groups was varied in order to estimate the effects of worker interactions. Though the group phenotype was mainly determined by additive interactions, nonlinear effects were also found. Mixed worker groups, combined from colonies with similar reactivity in the bioassay, showed a stronger response than pure groups. This phenomenon, analogous to the overdominance model for individuals in classical genetics, has implications for mechanisms of natural and artificial selection in social populations and for the evolution of polyandry in social Hymenoptera.     

Experimental assessment of wind erosion after soil stabilization treatments at Eneabba,Western Australia

Wind tunnel experiments on rehabilitation surfaces at Eneabba, Western Australia evaluated the techniques used by Associated Minerals Consolidated Ltd. (AMC) and Allied Eneabba Ltd. (AEL) to stabilize regions being revegetated following heavy mineral sand mining. Newly landscaped areas proved to be the most erodible, beginning to erode at 9 m sec⁻¹ and producing a soil flux of 10 kg m⁻¹ min⁻¹ at 18 m sec⁻¹ wind speeds. Sandier, more organically-rich, surfaces in the rehabilitation areas were somewhat less erodible with losses of only 2 kg m⁻¹ min⁻¹ at wind speeds of 18 m sec⁻¹. The mining companies use various nurse crops and top dressing mulch for surface stabilization. Rows of oats, sparse plantings of the grass cultivar “SUDAX” (Dekalb ST6) supplied by Westfarmers Ltd. and applications of Terolas, a cold, bituminous surface binding material supplied by Shell Co. of Australia Ltd., all proved successful in reducing wind erosion in this semi-arid region where more than 25% of summer days experience winds greater than 8 m sec⁻¹.     

The critical level of cadmium in renal cortex: the concept and its limitations

Because renal cortex is a primary target organ of Cd the seriousness of human exposure is commonly assessed in terms of the extent to which it permits renal cortical Cd concentrations to approach a critical value. The critical value has been defined in terms of PCC-10, the population critical concentration at which 10% of exposed individuals may be expected to show abnormal renal function. In chronically exposed human populations, PCC-10 appears to lie in the range of 180 to 220 μg Cd/gram fresh weight of cortex. However, Cd accumulated in the kidney under these conditions is distributed between more than one compartment, in all likelihood differing greatly in their toxicological characteristics. For instance, a major fraction of this Cd is bound to metallothionein, and may as such be relatively inert. Compartmentation of tissue Cd, in turn, is strongly influenced by the nature of exposure, and the PCC-10 value of 200 μg/g may therefore have limited general significance. The problem of risk assessment is further complicated by the high variability of Cd absorption. Nevertheless, human renal Cd levels commonly reach values as high as 1/3 to 1/6 of the chronic PCC-10, and further increases in Cd intake should therefore be avoided.     

Effect of detrital nutritional quality on population dynamics of a marine nematode (Diplolaimella chitwoodi)

The quantity and nutritional quality of detritus significantly affected the population growth rate (r) and carrying capacity (K) of Diplolaimella chitwoodi (Nematoda) in laboratory cultures. The rate of increase (r) was roughly constant for cultures fed Ulva fasciata, Pablum, Gracilaria foliifera and one Spartina alterniflora detritus, but was lower for Thalassia testudinum detritus and another S. alterniflora detritus. Rate of increase was unaffected by amount of food supplied except for seaweed detritus where r was lower for lower ratios. Carrying capacity (K) was strongly affected by both detrital type and rate of food supply. The best predictor of K was the rate of nitrogen supply to these cultures implying that natural populations may be N-limited. The nitrogen content of detritus appears to be the best measure of its nutritional quality.     

Spatial distribution of the infaunal benthic communities of the Ría de Muros,north-west Spain

Benthic samples were collected at 13 stations in the Ría de Muros, north-west Spain. There are three major communities: (1) in the southern and outer part of the ría, an Amphiura filiformis—Thyone fusus community, inhabiting sandy sediments with low organic content; (2) in the middle part of the ría, and Amphiura chiajei—Maldane glebifex community, inhabiting muddy sediments that are not anoxic (sulphide not detected); (3) in Muros Bay and the inner part of the ría, a Spiochaetopterus costarum community, inhabiting anoxic sediments with high organic content. Biomass is very high (up to 46.2 g ash-free dry wt) in the first two communities. In the Spiochaetopterus costarum community, biomass and diversity are much lower, probably because of oxygen deficiency.     

A new method for estimating phytoplankton growth rates and carbon biomass

A new method is described for the determination of phytoplankton growth rates and carbon biomass. This procedure is easy to apply and utilizes the labeling of chlorophyll a (chl a) with ¹⁴C. Pure chl a is isolated using two-way thin-layer chromatography, and the specific activity of chl a carbon is determined. Data from laboratory cultures indicate that the specific activity of chl a carbon becomes nearly equal to that of total phytoplankton carbon in incubations lasting 6 to 12 h and can be used to calculate phytoplankton growth rates and carbon biomass. Application of the method to the phytoplankton community in an eutrophic estuary in Hawaii indicates that the cells are growing with a doubling time of about 2 d and that about 85% of the particulate carbon consists of phytoplankton carbon.