An exploration of factors influencing lotic insect species richness

An understanding of factors that influence species richness of lotic insects is generally lacking. We present comparative data on aquatic insect species richness from several North American and other streams. Factors such as large sample numbers and drainage area (species area relationships) are not significant predictors of species richness across the streams we examined. We explore several hypotheses regarding the origins and maintenance of species richness using Upper Three Runs Creek (UTR), South Carolina, USA, as a reference stream. UTR has the highest species richness of any stream in the Western Hemisphere. Hypotheses examined included historical, regional and local processes such as: (1) Evolutionary time, (2) disturbance regime/environmental variability, (3) temperature/evolutionary-speed, (4) productivity, and (5) habitat heterogeneity. Of these hypotheses, we suggest that productivity and habitat heterogeneity appear to contribute most to the high species richness found in UTR. We believe that multidisciplinary analysis of other streams is necessary because without this crucial information our knowledge of, and desire to protect biodiversity in streams will be wanting.     

The microdistribution of some lotic insect predators in relation to their prey and to abiotic factors

SUMMARY. 1. The microdistribution of three species of insect predators in a Swedish stream was assessed using a multivariate statistical approach. Both abiotic factors and factors pertaining to the prey community were included in the analysis.
2. The factors most strongly correlated to the distribution of large Dinocras cephalotes were the densities of case less caddis larvae ( Wormaldia sp. and Hydropsyche siltalai ) and the median weight of stonefly prey. For small D. cephalotes , the density of H. siltalai and the percentage of moss cover were most important. Isoperla grammatica showed a significant correlation to blackfly density. Rhyacophila nubila occurred predominantly in patches with high prey biomass and with high densities and median weight of case less caddis larvae.
3. It was concluded that the quantity and quality of the prey, such as size, availability and species, influenced the predators'microdistribution. The distributional pattern differed between species of predators and was probably related to their different hunting strategies.     

Similarities in feeding behaviour between some marine and freshwater fishes in two tropical communities

The feeding behaviour and diets of fishes in two tropical habitats, a marine reef and a freshwater pond, were studied comparatively in Brazil. Similarities were found in the tactics employed to obtain food, the social patterns during foraging, and the general diet, notwithstanding lower-level taxonomic differences between the food items. The feeding behaviours of about one-third of the fish fauna from each community were approximately equivalent. The feeding categories of these fishes are briefly described. The similarities in the feeding modes probably reflect structural and functional properties shared by the two communities. Additional behavioural similarities of fishes in both habitats are presented and the lack of some particular foraging modes in each community is noted. The picture emerged that different, unrelated fish assemblages have the ability to evolve towards a similar behavioural and structural organization in response to comparable situations and constraints. The value of underwater observations and naturalistic studies on tropical freshwater fish assemblages is indicated.     

The ontogeny of feeding behaviour in four species of centrarchid fish

Relatively little work has been done on the ontogeny of feeding behaviour in fish. One of the aims of this study was to compare the ontogeny of feeding behaviour in four species of centrarchid fish of diverse feeding guilds. A second aim was to test Mayr's hypothesis that the locomotory acts involved in the ontogeny of feeding behaviour would be stereotyped. All four species initially displayed five feeding acts, with three of the acts disappearing from the repertoire at various intervals. The disappearance of the acts appeared to be related to the size and not to the age of the fry. The acts decreased in frequency as the fry aged and differences among the species in frequencies were minimal. The data supported Mayr's hypothesis but a modifying corollary was added to account for changes due to maturation.     

Growth rate plasticity to temperature in two damselfly species differing in latitude: contributions of behaviour and physiology

Plasticity in growth rate may be driven by behavioural and physiological mechanisms. Although these underlying mechanisms have direct implications for the importance of ecological and physiological costs associated with rapid growth, the contribution of behaviour and physiology to temperature-mediated plasticity in growth rate has largely been neglected. We studied the temperature-dependence of growth rate and its underlying behavioural and physiological mechanisms in two congeneric damselfly species that differ in latitudinal distribution. Larvae were reared from the egg stage at three temperatures (17°C, 22°C and 27°C). Within each species, growth rates showed a quadratic response curve with an optimum at 22°C. Behaviour, as measured by food intake, and physiology, as measured by growth efficiency and heartbeat as proxy for metabolic rate, jointly contributed to this temperature-induced plasticity in growth rate. At each temperature, growth rates were higher in the northern species. In line with the few other studies that compared northern and southern populations, both an increased food uptake and growth efficiency caused this pattern. Together with previous studies that focused on the population level, our results tentatively suggest that not only the latitudinal patterns in growth rate but also the mechanistic basis are similar at the species and at the population level.     

The functional responses of two benthic algivorous ciliated protozoa with differing feeding strategies

Surface-associated algivorous ciliated protozoa are common in the benthos of streams, but little is known about the feeding ecology of these organisms. We compared the functional responses of two algivorous ciliated protozoa, Oxytricha fallax (a filter feeder) and Trithigmostoma cucullulus (an encounter feeder). The ciliates were fed ¹⁴C-labeled Navicula cryptocephala in laboratory feeding experiments to determine their potential to consume significant amounts of algal prey. Logistic regression, and plots of the proportion of N. cryptocephala ingested vs. the total number offered, indicated functional responses of a typical rectangular hyperbolic (type II) form for both ciliates. Ingestion rates were estimated from regressions of the number of ¹⁴C-labeled N. cryptocephala cells ingested per ciliate vs. time. Maximum feeding rates and half-saturation concentrations were estimated by fitting the observed ingestion rates and experimental algal densities to a function of the Michaelis-Menten enzyme kinetics form using nonlinear regression. For O. fallax, the maximum feeding rate was estimated to be 1.07 N. cryptocephala cells per minute, and the half-saturation concentration was 3.9 × 102 N. cryptocephala per square centimeter. For T. cucullulus the maximum feeding rate was estimated to be 0.2 N. cryptocephala per minute, and the half-saturation concentration was 5.4 × 10³N. cryptocephala per square centimeter. The data were also fitted using only the number of cells ingested at 60 and 120 min, by converting the endpoint consumption to rates. For O. fallax, the estimated maximum feeding rates were 1.3 and 1.0 N. cryptocephala per minute for 60 and 120 min, respectively, and estimated half-saturation concentrations were 5.1 × 10² and 3.5 × 10²N. cryptocephala per square centimeter. For T. cucullulus, estimated maximum feeding rates were 0.6 and 0.4 N. cryptocephala per minute for 60 and 120 min, respectively, and estimated half-saturation concentrations were 1.5 × 10⁴ and 1.1 × 104 N. cryptocephala per square centimeter. These results suggest that kinetic methods for estimating ingestion rates are more accurate than endpoint determinations. Based on field observations of periphyton densities, these ciliates potentially are consuming 4.8% of the total available standing crop of diatom biomass per day and this could represent up to 16% of total available daily primary production.     

The life cycles of three species of Ephemeroptera in two streams in Poland

Nymphs of Rhithrogena iridina, Baetis alpinusand Baetis melanonyx were collected in theWoosatka and Terebowiec streams; Bieszczady NationalPark, southeastern Poland. The streams have differentenvironmental conditions. The life cycles of Rhithrogena iridina in the Woosatka and theTerebowiec streams were of the univoltine winter type.In the Woosatka (Station 1) this species had aunivoltine life cycle with one cohort. In theTerebowiec (Station 2), R. iridina had aunivoltine life cycle with two cohorts – winter andsummer. The development of Baetis alpinus tookvarious courses depending on environmental conditions.At the lower station (Woosatka), where watertemperature reached higher values and the stream bedis less shady, the species had a winter-summer cyclewith two generations a year. At the higher station,(Terebowiec) it likely had a winter cycle with one ortwo generations. Baetis melanonyx had summercycles with one generation at both stations.     

Taxonomy of some common Amphidinium species

The taxonomic status of several well known species belonging to the genus Amphidinium (Dinophyceae) has been re-examined. Studies in culture and observations on the micro-anatomy of these organisms suggest that the number of species can be reduced to two, A. klebsii and A. carterae. They may be distinguished on the basis of fundamental differences in chloroplast morphology.     

Immunocytochemical localization of trehalase inhibitor in some insect species

Antibody against cockroach trehalase inhibitor was prepared and tested against the plasma of adult locusts and larval silkworms to determine whether these species possess a similar protein. An immunopositive response was elicited in both species. Studies using immunogold labeling show that adult cockroaches have trehalase inhibitor protein in granules of plasmatocytes and in oenocytoid-like structures. Localization of the immunoreactive protein with trehalase inhibitor antibody in locust hemocytes indicated that the protein is also contained in the granules of plasmatocytes. However, in the hemolymph of silkworm larvae, the immunoreactive protein was found only in the spherules of spherulocytes. The results suggest that insect hemolymph commonly contains trehalase inhibitor both in plasma and in certain hemocytes.     

Multimodal sensory organs in larvae of some insect species

The morphological diversity of antennal sensory organs in larvae of Galeruca sp. (Coleoptera, Chrysomelidae), Limnephilus centralis (Trichoptera, Limnephilidae), and Eristalis tenax (Diptera, Syrphidae) was studied. A sensory cone on the antenna was found in all the species studied. The cuticular part of the antennal cone is pierced with pores. No significant differences in the shape of the antennal cone were revealed. The innervation patterns of the antennal cone varied from single cells in the leaf beetle larvae to groups of cells with a common scolopoid sheath in the fly larvae. The cone combines several types of sensilla that perform mechanoreceptor, olfactory, and gustatory functions. The morphology and ultrastructural organization of the antennal cone in relation to the heterogeneity of the larval habitats are described.     

The importance of predation,substrate and spatial refugia in determining lotic insect distributions

An experiment was conducted to evaluate the interaction between predation, substrate, and spatial refugia in the organization of a stream insect community (Reeds Creek, Pendleton Co., West Virginia). Patterns of insect colonization were compared between fish exclusion cages and open controls that allowed access to vertebrate predators. Each cage contained 4 different substrates that varied in the relative amount of spatial refugia. Fish had little influence on the diversity or abundance of any insect taxa, even when spatial refugia were limited. The only significant effect due to predation, was an increased diversity of large (>8 mm) invertebrates in the absence of predators. However, because these taxa were relatively rare, the overall role of fish predation on insect community structure was minimal.In contrast, substrate had a marked effect on insect colonization. Insects were always more abundant (number/basket) on loose substrates containing large numbers of interstitial spaces, compared to cement-embedded substrates with few refuges available. In addition, invertebrates were more abundant on loose gravel compared to loose cobbles. Howver, when substrate preferencesrd were examined according to insect density (number/m²), loose cobbles were generally the preferred substrate. The present experiment rejects the hypothesis that patterns of substrate colonization can be explained as differential insect mortality by predators, due to varying amounts of refugia. Alternative mechanisms such as differing amounts of trapped detritus and substrate surface area may account for substrate preference.     

Mate-guarding in a promiscuous insect: species discrimination influences context-dependent behaviour

Mating strategy is often informed by social context. However, information on social environment may be sensitive to interference by nearby heterospecifics, a process known as reproductive interference (RI). When heterospecific individuals are present in the environment, failures in species discrimination can lead to sub-optimal mating behaviours, such as misplaced courtship, misplaced rivalry behaviours, or heterospecific copulation attempts. All aspects of mating behaviour that are influenced by social context may be prone to RI, including copulatory behaviours associated with mate-guarding in the presence of possible competitors. Here we investigate the effect of three heterospecifics on the mate-guarding behaviour of male Lygaeus equestris seed bugs. We find that, despite previously reported heterospecific mating harassment amongst these species of lygaeid bug, male L. equestris are able to effectively distinguish rival conspecific males from heterospecifics. Thus, heterospecific mating attempts in this group may reflect selection on males to mate opportunistically, rather than a failure of species discrimination.     

ATP-driven proton pumping in two species of Chara differing in salt tolerance

Chara corallina is an obligate freshwater alga, while C. buckellii can be grown in salt and freshwater culture. When grown in fresh water, C. buckellii has electrophysiological properties similar to C. corallina, but when cultured in salt water, it has a less negative membrane potential and has a higher conductance. We show in internally perfused, tonoplast-free cells that the ATP-dependence of the two species cultured in fresh water is similar, although C. buckellii hyperpolarizes at lower ATP concentrations. We determined the pump parameters in perfused and intact cells. Using both techniques, C. corallina and C. buckellii cultured in fresh water show similar values of E_p, G_p and I_p. However, there is a significant difference between the two techniques: E_p is more negative (–400 to –700 mV) in perfused cells than in intact cells (–220 to –260mV); G_p is lower (0·1–0·2 versus 0·3–0·9 S m^?2); and I_p is higher (40–60 versus 10–18 mA m^?2). Salt-cultured C. buckellii was compared with freshwater C. buckellii using intact cells; G_p and E_p were similar, but I_p was much higher in salt-cultured cells (60 versus 15mA m^?2). This higher pump rate is due to the depolarization of the membrane of salt-cultured algae, which is caused by a higher passive conductance. The significance of the less negative membrane potential and the higher rate of proton pumping is discussed with respect to the banding pattern and salt stress.     

Development of two isogenic sweet corn hybrids differing for glycinebetaine content

A hybrid of sweet corn, Zea mays L. (`1720'; Rogers Brothers Seed Co.), was found to be comprised of glycinebetaine-positive and glycinebetaine-deficient individuals in a 1:1 mixture. This phenomenon was traced to segregation for a single, nuclear, dominant gene determining leaf glycinebetaine content within the female inbred parent of this hybrid. Selection for homozygous recessive (glycinebetaine-deficient) and homozygous dominant (glycinebetaine-positive) genotypes of the female inbred parent enabled production of two isogenic versions of hybrid `1720' differing with respect to a single copy of the dominant allele, by mating these female parent selections with the common homozygous recessive (glycinebetaine-deficient) male parent. These two isogenic hybrids are shown to differ by a factor of 300- to 400-fold in glycinebetaine titer of young expanding leaves of salinized plants, but exhibit no striking differences in the levels of free amino acids or the level of N-methylnicotinic acid (nicotinic acid betaine; trigonelline). The only significant difference between the two hybrids in terms of amino acid composition was found to be in the level of alanine under nonsalinized conditions. The betaine-deficient hybrid exhibited a 14% lower alanine level than the betaine-positive hybrid. Betaine deficiency was not associated with altered stress-induced accumulation of amino acids such as proline, serine, and asparagine plus aspartate, attesting to the high specificity of the genetic difference between these isogenic hybrids with respect to betaine accumulation. This germplasm offers unique opportunities to test whether a single dominant allele determining stress-induced betaine accumulation capacity influences stress resistance in maize.     

Effects of cotton cultivars differing in gossypol content on the quality of Aphis gossypii as prey for two species of Coccinellidae

Plants can have detrimental effects on biological control agents by affecting their prey or host quality. Thus, it is important to understand the tri-trophic interactions between plants, herbivores and natural enemies when implementing biological control programmes. Studies have shown that both morphological and chemical traits of host plants can affect the third trophic level. Cotton plants are known to produce alkaloids such as gossypol, a sesquiterpene aldehyde that can confer resistance against herbivorous arthropods. Nevertheless, little is known about the effect of gossypol on biological control agents. In this study, we investigated how three cotton cultivars (BRS Rubi, BRS Safira and BRS Verde) differing in gossypol content affect development and growth of predatory coccinellids, Eriopis connexa and Harmonia axyridis, feeding on the cotton aphid Aphis gossypii reared on those cultivars. The results show that the cultivar BRS Rubi (highest gossypol content) had a sub-lethal effect on the development and growth of both Coccinellidae species compared with the other cultivars. Overall, the cultivar BRS Rubi reduced slightly fecundity, net reproductive rate and intrinsic rate of natural increase for both Coccinellidae species. However, because aphid populations stay short periods of time in the field, and adult coccinellids may supplement its diet with alternative prey and plant material this sub-lethal indirect effect of gossypol may not have a detrimental effect on field biological control of cotton aphid by either E. connexa or H. axyridis, thus suggesting a compatibility between plant resistance and biological control agents.     

The feeding behaviour of New Zealand Dolomedes species (Araneae: Pisauridae)

Abstract

The prey spectrum and predatory behaviour of Dolomedes sp. (‘D. III’), D. aquaticus, and D. minor are described from a series of field and laboratory investigations, the former made around Nelson and on Banks Peninsula, Canterbury, during summer months. All species are large, robust spiders that capture prey by directly seizing it in their mouthparts, not using silk at any stage of predation. Adult aquatic insects are their main prey, but these are available only irregularly during their activity period (night-time), and the spiders are opportunistic in their feeding habits. They will eat virtually any available small animal, and at least the largest species, D. III, is able to capture and ingest small fishes. Dead as well as live organisms are taken. Furthermore, the spiders are capable of feeding infrequently; when feeding on small prey organisms they may capture several sequentially, to increase the size of the meal. Live prey is caught while it is in flight, or on the ground, or at the water surface (rarely submerged), and is detected primarily by touch and airborne sound; vision is unnecessary for normal predation. Prey is captured very rapidly, even though this may initially involve a dash of up to 40 cm across the water surface to locate the organism. Stages in the behaviour of an active spider, from waiting for prey to grooming after ingestion, are described.