Early development of johnny darter,Etheostoma nigrum,and fantail darter,E. flabellare,with a discussion of its ecological and evolutionary aspects

Synopsis Fantail darters,Etheostoma flabellare, have larger eggs with greater yolk volume than johnny darters,E. nigrum, and have a longer embryo period. This longer embryo period is associated with accelerated finfold differentiation, producing a larger, better formed individual at the onset of exogenous feeding. Developmental differences among these two species and the rainbow darter,Etheostoma caeruleum, primarily in timing of ontogenetic events, are described in detail. These differences in timing are considered largely early developmental phenomena as they affect embryos, larvae, and aievins but apparently not juveniles or adults. Demographic aspects of early life history were assessed using data from studies of Ontario streams. Differences in early survival among species appear to play an important role in recruitment of mature females, but cannot be attributed to parental care or egg size differences.     

Temperature selection and critical thermal maxima of the fantail darter,Etheostoma flabellare,and johnny darter,E. nigrum,related to habitat and season

Synopsis Riffle dwelling fantail darters (Etheostoma flabellare) selected lower temperatures in winter (19.3°C) compared to pool dwelling johnny darters (E. nigrum; 22.0°C. A similar trend was evident in summer tests (fantail darters, 20.3°C; johnny darters, 22.9°C). Summer tested animals selected higher temperatures than winter tested animals maintained at the same acclimation temperature and photoperiod. When tested together in the same gradient, both species appeared not to thermoregulate, but tended to avoid each other. Critical thermal maxima (CTMax) did not differ between seasons for either species (fantail darters, 31.1°C winter, 31.3°C summer; johnny darters, 30.9°C winter, 30.5°C summer). Differences in the thermal responses of these darters correlated with differences in their respective habitats.     

Living on the bottom: Kinematics of benthic station‐holding in darter fishes (Percidae: Etheostomatinae)

Darters represent a substantial radiation of freshwater fishes that live in close association with the substrate in North American streams and rivers. A key feature of any darter species is therefore its ability to stay in place or to “hold station” in flowing water. Here, we quantify the station‐holding performance of two morphologically divergent darter species, the fantail darter Etheostoma flabellare and the Missouri saddled darter Etheostoma tetrazonum. We also characterize the primary kinematic responses of the two species when holding station in flow speeds ranging from 4 to 56 cm s^?1 in a flow tank on either plexiglas or small rock substrate. We then present a series of hypotheses about the potential hydrodynamic and functional consequences of the observed postural changes and the links among morphology, posture, and station‐holding performance. On both substrates, E. tetrazonum was able to hold station at higher flow speeds than E. flabellare. On rocks, E. tetrazonum slipped at an average speed of 55.7 cm s^?1 whereas E. flabellare slipped at 40.2 cm s^?1. On plexiglas, E. tetrazonum slipped at an average speed of 24.7 cm s^?1 whereas E. flabellare slipped at 23.1 cm s^?1. We measured body and fin positions of the two species from individual frames of high‐speed video while holding station on rocks and plexiglas. We found that on both substrates, the two species generally exhibited similar kinematic responses to increasing flow: the head was lowered and angled downward, the back became more arched, and the median and caudal fin rays contracted as water flow speed increased. The ventral halves of the pectoral fins were also expanded and the dorsal halves contracted. These changes in posture and fin position likely increase negative lift forces thereby increasing substrate contact forces and reducing the probability of downstream slip. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Spatiotemporal variability of stream habitat and movement of three species of fish

Relationships between environmental variability and movement are poorly understood, due to both their complexity and the limited ecological scope of most movement studies. We studied movements of fantail (Etheostoma flabellare), riverweed (E. podostemone), and Roanoke darters (Percina roanoka) through two stream systems during two summers. We then related movement to variability in measured habitat attributes using logistic regression and exploratory data plots. We indexed habitat conditions at both microhabitat (i.e., patches of uniform depth, velocity, and substrate) and mesohabitat (i.e., riffle and pool channel units) spatial scales, and determined how local habitat conditions were affected by landscape spatial (i.e., longitudinal position, land use) and temporal contexts. Most spatial variability in habitat conditions and fish movement was unexplained by a site’s location on the landscape. Exceptions were microhabitat diversity, which was greater in the less-disturbed watershed, and riffle isolation and predator density in pools, which were greater at more-downstream sites. Habitat conditions and movement also exhibited only minor temporal variability, but the relative influences of habitat attributes on movement were quite variable over time. During the first year, movements of fantail and riverweed darters were triggered predominantly by loss of shallow microhabitats; whereas, during the second year, microhabitat diversity was more strongly related (though in opposite directions) to movement of these two species. Roanoke darters did not move in response to microhabitat-scale variables, presumably because of the species’ preference for deeper microhabitats that changed little over time. Conversely, movement of all species appeared to be constrained by riffle isolation and predator density in pools, two mesohabitat-scale attributes. Relationships between environmental variability and movement depended on both the spatiotemporal scale of consideration and the ecology of the species. Future studies that integrate across scales, taxa, and life-histories are likely to provide greater insight into movement ecology than will traditional, single-season, single-species approaches. The Virginia Cooperative Fish and Wildlife Research Unit is jointly sponsored by the US Geological Survey, Virginia Polytechnic Institute and State University, Virginia Department of Game and Inland Fisheries, and Wildlife Management Institute.     

Ecological and evolutionary consequences of early ontogenies of darters (Etheostomatini)

Synopsis The ecological classification of fishes into reproductive guilds is based on the premises that (1) reproductive styles and early ontogeny are closely related, and (2) both are correlated with the ecology of a species. A comparison of early ontogenies of logperch (Percina caprodes), rainbow darter (Etheostoma caeruleum), and fantail darter (E. flabellare) confirmed these premises, and provided possible explanations for diversity within the Etheostomatini. Young logperch have limited vitelline circulation, hatch while still poorly developed, and therefore must drift from oxygen rich lotic habitats to lentic habitats where small planktonic prey are available. Young rainbow and fantail darters have extensive vitelline plexuses, are well developed at transition to first feeding, and begin feeding on aquatic insects. Thus there is no necessity for a drift interval. As a result, the latter species are adapted for stream life. Interspecific differences in reproductive styles and early ontogenies may have contributed to speciation of darters by allowing partitioning of breeding sites and food resources for young. In addition, reduced drift dispersal and small stream habitation may have indirectly contributed to speciation by reducing genetic exchange among populations.     

Feeding ecology of three predacious aquatic insects and two fish in a riffle of the Speed River,Ontario

The food habits of two fish (Etheostoma flabellare and Rhinichthys atratulus) and three predacious aquatic insects (Nigronia serricornis, Paragnetina media and Agnetina capitata) were examined for one year in a riffle of the Speed River, Ontario. Adult E. flabellare fed primarily on net-spinning caddisflies whereas juvenile E. flabellare relied heavily on chironomids. Rhinichthys atratulus had a more varied diet composed of chironomids, Antocha larvae (Tipulidae) and net-spinning caddisflies. Two of the aquatic insect predators consumed large numbers of net-spinning caddisflies; however, P. media contained large percentages of Hydropsyche and Cheumatopsyche whereas N. serricornis fed primarily on non-hydropsychid net-spinners. The diet of A. capitata was composed largely of chironomids and mayflies. Schoener's diet overlap index () suggested that large E. flabellare and P. media had similar diets; however, E. flabellare ingested much larger prey than P. media. Adult E. flabellare contained a significantly greater proportion of larger prey items in comparison with benthic samples whereas similar comparisons with other predators showed no selection for larger prey. These data demonstrate that E. flabellare was size selective given the range of prey sizes available whereas the other predators were not. Also, there was little dietary overlap among the fish and invertebrate predators suggesting a partitioning of resources.     

Temporal and spatial patterns of spawning site use by two cavity-spawning darters in a Wisconsin stream

Synopsis There was partial spatial and complete temporal overlap of spawning by Etheostoma flabellare and E. nigrum in Marsh Creek, Wisconsin. E. flabellare tended to spawn at shallower depths than E. nigrum. Both species spawned over a greater range of depths in an area with few spawning sites (cavities under rocks or logs) than in an area where spawning sites were abundant. In the laboratory E. flabellare were able to prevent E. nigrum from occupying cavities they would have otherwise occupied. E. nigrum appear to be competitively inferior to E. flabellare in terms of spawning-site acquisition and retention, but possess several attributes that may allow them to persist in the presence of the latter.     

Limiting similarity and the intensity of competitive effects on the mottled sculpin,Cottus bairdi,in experimental stream communities

The identification of potential competitors has been driven by the concept of limiting similarity. Lacking are explicit tests of interaction strength among morphologically similar and dissimilar species. I used the mottled sculpin, Cottus bairdi, as a focal species in an artificial stream experiment designed to compare the effect of intraspecific competition to interspecific cometition from two very different species: a congener, the Kanawha sculpin (C. carolinae ssp.), and an unrelated species, the fantail darter (Etheostoma flabellare). The differences in morphology between these two species generate specific predictions under limiting similarity regarding the likelihood of competition and its relative strength: the congener should be a more important potential competitor. Increased fish density had a strong effect on the multivariate response of survival and growth, and on the relative condition of C. bairdi, indicating competition. The effect of additional C. bairdi or Kanawha sculpins were roughly equal, but the effect of E. flabellare was significantly greater. The most important potential impact on C. bairdi came from interspecific competition by a species that is smaller and very different in morphology, contrary to predictions based on limiting similarity.     

Seasonal colour and antipredator behaviour in Etheostoma (Percidae)

This study examined how colour varies across season and sex in the fantail darter Etheostoma flabellare and the banded darter Etheostoma zonale. Etheostoma flabellare has male‐only parental care and exhibited slight sexual dimorphism in overall colour, with no discernible effect of season on colour; whereas E. zonale does not have parental care and exhibited substantial sexual dimorphism in colour, but only in the breeding season. Additionally, antipredator behaviour of E. zonale was compared between males that were fully coloured during the breeding season and males that were partially coloured at that time, but the effects of colour and season were not consistent across males.     

Assessment of Predation Risk by Juvenile Yellow Perch, Perca flavescens: Responses to Alarm Cues from Conspecifics and Prey Guild Members

In two laboratory experiments we tested juvenile yellow perch, Perca flavescens, for behavioural responses to alarm cues of injured conspecifics and several prey guild members: adult perch, Iowa darters, Etheostoma exile and spottail shiners, Notropis hudsonius. Spottail shiners are phylogenetically distant to yellow perch whereas Iowa darters and perch are both members of the Family Percidae. Groups of juvenile yellow perch increased shoal cohesion and movement towards the substrate after detecting conspecific alarm cues when compared to cues of injured swordtails, Xiphophorus helleri, a species phylogenetically distant from perch. Individual juvenile perch increased shelter use and froze more when exposed to chemical alarm cues from both juvenile and adult perch, shiners and darters compared to exposure to injured swordtail cues or distilled water. The response to cues of darters may indicate that alarm cues are evolutionarily conserved within percid fishes or that perch had learned to recognize darter cues. The response to spot tail shiners likely represents learned recognition of the cues of a prey guild member.     

Ontogeny of critical and prolonged swimming performance for the larvae of six Australian freshwater fish species

Critical (<30 min) and prolonged (>60 min) swimming speeds in laboratory chambers were determined for larvae of six species of Australian freshwater fishes: trout cod Maccullochella macquariensis, Murray cod Maccullochella peelii, golden perch Macquaria ambigua, silver perch Bidyanus bidyanus, carp gudgeon Hypseleotris spp. and Murray River rainbowfish Melanotaenia fluviatilis. Developmental stage (preflexion, flexion, postflexion and metalarva) better explained swimming ability than did length, size or age (days after hatch). Critical speed increased with larval development, and metalarvae were the fastest swimmers for all species. Maccullochella macquariensis larvae had the highest critical [maximum absolute 46·4 cm s^?1 and 44·6 relative body lengths (L_B) s^?1] and prolonged (maximum 15·4 cm s^?1, 15·6 L_B s^?1) swimming speeds and B. bidyanus larvae the lowest critical (minimum 0·1 cm s^?1, 0·3 L_B s^?1) and prolonged swimming speeds (minimum 1·1 cm s^?1, 1·0 L_B s^?1). Prolonged swimming trials determined that the larvae of some species could not swim for 60 min at any speed, whereas the larvae of the best swimming species, M. macquariensis, could swim for 60 min at 44% of the critical speed. The swimming performance of species with precocial life‐history strategies, with well‐developed larvae at hatch, was comparatively better and potentially had greater ability to influence their dispersal by actively swimming than species with altricial life‐history strategies, with poorly developed larvae at hatch.     

Selective predation by four darter (Percidae) species on larval chironomids (Diptera) from a Mississippi stream

We determined seasonal foraging modes of four sympatric darter species, Etheostoma lynceum, E. stigmaeum, E. swaini and Percina nigrofasciata, from Beaverdam Creek, Mississippi (USA) at two scales of taxonomic resolution: (1) chironomid prey identified to family and (2) chironomid prey identified to genus/species. When chironomids were identified to family, high proportional similarity (PS) and low niche breadth (NB) values suggested the darters fed opportunistically on a relatively small number of available prey taxa. In contrast, when chironomids were identified to genus/species, concordant low PS and NB values suggested the darters fed like classic specialists, selecting a small number of prey taxa relative to prey availability in the resource base. The darters selected just one to four chironomid taxa from 52 available taxa across seasons. Our study shows that the scale of taxonomic resolution used to identify darter prey may influence the characterization of darter foraging modes.     

Effects of Barriers and Thermal Refugia on Local Movement of the Threatened Leopard Darter, Percina pantherina

Local, short-term dispersal by the U.S. federally-threatened leopard darter, Percina pantherina, was examined in the field and in the laboratory to assess the possible effects of natural versus man-made barriers on movement. Mark-resight studies were conducted in two summers at sites in the Glover River (southeastern Oklahoma, U.S.A.). At one site, patches of 'preferred' habitat were separated by a natural riffle; at the other site, by a low-water road crossing with culverts. At the Natural Riffle site, darters moved downstream across the riffle, but also moved upstream into deeper water when water temperatures exceeded 29°C in the `preferred' habitat. Use of deeper, cooler waters by this species in late summer suggests that thermal refugia may be important habitats for the long-term management of leopard darters. At the Road Crossing site, all documented movement was in a downstream direction, and at least two darters traversed culverts in the low-water bridge. Laboratory studies of movement across several types of culverts suggested that culverts significantly decrease the probability of movement among habitat patches.     

Hunting flight speeds of five southern African raptors

The flight speeds of hunting falconry birds were determined using global positioning system data loggers. Until now, the hunting flight speed of African raptors has not been directly measured. We predicted that hunting flight speeds would differ between species and that flight dynamics, such as altitude, and bird morphology, particularly wing surface area, would influence maximum and mean flight speeds. This study considered five African raptor species, which included two long-wing species, Lanner Falcon Falco biarmicus and Peregrine Falcon F. peregrinus, one short-wing species, Black Sparrowhawk Accipiter melanoleucus, and two broad-wing species, African Hawk-eagle Aquila spilogaster and Jackal Buzzard Buteo rufofuscus. Maximum and mean hunt speeds differed significantly between the long- and short-wing species. There was no difference in acceleration or deceleration rates between these species, but this could be due to small sample sizes. There was a significant positive correlation between maximum hunt speed and maximum flight height for the long-wing species. Maximum and mean flight speeds were significantly negatively correlated with wing area for all five species in this study. However, following phylogenetic correction, no significant relationship between wing area and maximum hunt speeds was found. This study presents baseline data of hunting speeds in African raptors and further highlights the importance of inter-species variation, which can provide accuracy to flight speed models and the understanding of hunting strategies.     

Influence of riffle characteristics,surficial geology,and natural barriers on the distribution of the channel darter, <Emphasis Type="Italic">Percina copelandi,</Emphasis> in the Lake Ontario basin

Synopsis The channel darter, Percina copelandi, is a small benthic fish with a wide but disjunct distribution across central North America. The development of conservation and recovery strategies for Canadian populations is limited by a lack of knowledge regarding ecology, population size and other factors that affect its distribution and abundance. We sampled five rivers in the Lake Ontario basin to test whether the distribution of P. copelandi reflected riffle habitat characteristics or landscape-scale factors such as surficial geology and natural barriers (waterfalls). At most sites yielding P. copelandi, riffles flowed into deep sand bottomed run or pool habitats. Despite a lack of association with local surficial geology or riffle habitat characteristics, both the upstream limits of P. copelandi occurrence and distribution of suitable habitats reflected the distribution of waterfalls, chutes and bedrock outcroppings. In contrast to P. copelandi, distributions of Etheostoma flabellare, P. caprodes and Rhinichthys cataractae reflected among site differences in riffle habitat.     

Swimming patterns and behaviour of upriver-migrating adult pink (Oncorhynchus gorbuscha) and sockeye (O. nerka) salmon as assessed by EMG telemetry in the Fraser River,British Columbia,Canada

Little is known about the behaviour patterns and swimming speed strategies of anadromous upriver migrating fish. We used electromyogram telemetry to estimate instantaneous swimming speeds for individual sockeye (Oncorhynchus nerka) and pink salmon (O. gorbuscha) during their spawning migrations through reaches which spanned a gradient in river hydraulic features in the Fraser River, British Columbia. Our main objectives were to describe patterns of individual-specific swim speeds and behaviours, identify swimming speed strategies and contrast these between sexes, species and reaches. Although mean swimming speeds did not differ between pink salmon (2.21 BL s^–1) and sockeye salmon (1.60 BL s^–1), sockeye salmon were over twice as variable (mean CV; 54.78) in swimming speeds as pink salmon (mean CV; 22.54). Using laboratory-derived criteria, we classified swimming speeds as sustained (<2.5 BL s^–1), prolonged (2.5–3.2 BL s^–1), or burst (>3.2 BL s^–1). We found no differences between sexes or species in the proportion of total time swimming in these categories – sustained (0.76), prolonged (0.18), burst (0.06); numbers are based on species and sexes combined. Reaches with relatively complex hydraulics and fast surface currents had migrants with relatively high levels of swimming speed variation (e.g., high swimming speed CV, reduced proportions of sustained speeds, elevated proportions of burst speeds, and high rates of bursts) and high frequency of river crossings. We speculate that complex current patterns generated by river constrictions created confusing migration cues, which impeded a salmon's ability to locate appropriate pathways.     

Swimming performance and associated ionic disturbance of juvenile pink salmon Oncorhynchus gorbuscha determined using different acceleration profiles

Swimming performance was assessed in juvenile pink salmon Oncorhynchus gorbuscha (body mass <5·0 g) using five different protocols: four constant acceleration tests each with a different acceleration profile (rates of 0·005, 0·011, 0·021 and 0·053 cm s^?2) and a repeated ramped‐critical swimming speed test. Regardless of the swim protocol, the final swimming speeds did not differ significantly (P > 0·05) among swim tests and ranged from 4·54 to 5·20 body lengths s^?1. This result supports the hypothesis that at an early life stage, O. gorbuscha display the same fatigue speeds independent of the swimming test utilized. Whole body and plasma [Na⁺] and [Cl^?] measured at the conclusion of these tests were significantly elevated when compared with control values (P < 0·05) and appear to be predominantly associated with dehydration rather than net ion gain. Given this finding for a small salmonid, estimates of swim performance can be accurately measured with acceleration tests lasting <10 min, allowing a more rapid processing than is possible with a longer critical swim speed test.     

Sprint Speeds of Juvenile Scorpions: Among Family Differences and Parent Offspring Correlations

Sprinting from predators is an important part of the defensive repertoire of some scorpions. This study examined sprint speed in juvenile scorpions and its relation to sprint speed of the mothers. Sprint speeds of juvenile scorpions, Centruroides vittatus, were determined by repeated trials on a small racetrack. Speeds were repeatable across trials within individuals and differed among individuals. There were marked among family differences in juvenile sprint speeds. Juvenile sprint speeds were correlated with maternal sprint speeds. Although the effect of common maternal environment may inflate the measures of heritability to an unknown extent, these results suggest that sprint may respond to natural selection and there is an underlying genetic basis to observed performance differences among scorpions.     

Relationship between swimming capacities and morphological traits of fish larvae at settlement stage: a study of several coastal Mediterranean species

Experimental measurements were made in the laboratory to determine the swimming capacities of settlement-stage fish larvae of several Mediterranean coastal species collected from the nearshore waters of Corsica, France. Critical swimming speed (U_crit, cm s⁻¹) was measured to provide a realistic laboratory estimate of in situ swimming speed. Morphometric traits were measured to assess potential predictors of a species’ swimming ability and, when possible, daily otolith increments were used to estimate age. Observed swimming speeds were consistent with other temperate species and demonstrated that the tested species are competent swimmers and not passive components of their environment. Morphological traits varied in their correlation with U_crit across groups and species. Direct measurements of morphological traits were better predictors than calculated ratios. Pelagic larval duration had little relationship with swimming speed among species for which daily otolith increments were counted. In addition to expanding the database on swimming capacities of settlement-stage fish larvae in the Mediterranean Sea, this study also developed methods that simplify the assessment of larval fish swimming ability. Swimming speed data are essential for improving larval dispersal models and for predicting recruitment rates in coastal fish populations.