[Show abstract][Hide abstract] ABSTRACT: Molting is a stressful event in insect development. When an insect molts, the individual discards its exoskeleton and sheds and renews the interior lining of substantial portions of the respiratory (tracheal) system. We profiled for the first time the disruptive pattern of respiration during the molting process in larvae of the mayfly Cloeon dipterum (Ephemeroptera:Baetidae). Molting induces a precipitous drop in O-2 consumption immediately followed by a surge in O-2 consumption that appears to be compensatory in nature. Postmolt metabolic suppression is consistently observed during which O-2 consumption rates lag relative to those of nonmolting larvae. Furthermore, the magnitude of respiratory disturbance during the molt increases as a function of temperature. Increasing temperatures increase molting frequency and the apparently stressful nature of the molt itself. Thus, the insect molt appears to be a previously unappreciated route by which warming conditions may affect aquatic insects.
[Show abstract][Hide abstract] ABSTRACT: The genus Anaxipha has at least 13 North American species, eight of which are described here. Ten species fall into these three species groups: exigua group (exigua Say, scia Hebard and n. spp. thomasi, tinnulacita, tinnulenta, and tinnula); delicatula group (delicatula Scudder and vernalis n. sp.); litarena group (litarena Fulton and rosamacula n.sp.). The remaining three (imitator Saussure, fultoni n.sp., and calusa n.sp.) have no close relatives among the other species. Most new species were initially distinguished by their calling songs, and in most cases sympatric populations proved cleanly separable by features of male genitalia and tooth-counts of stridulatory files. Species groups were based mostly on comparisons of male genital structures and the results of DNA barcoding. Species are here characterized not only by their songs and morphology, but also by geographical, ecological, and seasonal distributions. At a given temperature the pulse rate (PR) of the male's calling song is a key aid to identification. PR at 25°C has a narrow range of variation within a species and among the 13 species its mean value varies from 5 to 79 p/s. As in other crickets, pulse rates plotted as a function of temperature have a positive, linear trendline. When trendlines for 11 Anaxipha species are extrapolated downward, the temperature at ŷ=0 p/s is 2.7+2.2 (mean±SD) — i.e., the lines tend to converge at about 3°C. This makes possible a simple formula for estimating the PR at 25°C from any Anaxipha calling song recorded at any temperature. Other aids to identifying species from their calling songs are the duration and regularity of breaks between pulse sequences and the relationship between PR and carrier frequency (CF). When CF is plotted as a function of PR, the relationship deviates noticeably from linear only in vernalis. We propose that in Anaxipha spp., as well as in six other genera in four gryllid subfamilies, the synchrony of tooth impacts and the fundamental vibrations of the CF is maintained by the scraper moving continuously over evenly spaced file teeth — rather than by the much-studied (and well-established) catch-and-release mechanism of Gryllus spp. Our proposal is based on the high rates of change in CF with temperature and on differences in the teeth of the stridulatory files. The PR at 25°C of each of the 13 species is remarkable in the degree to which it predicts the mean values of these five characters: file tooth number, tooth density, file length, pulse duration, and pulse duty cycle (Fig. 17). A neotype is designated for Gryllus pulicaria Burmeister (1838), the type species of the genus Anaxipha. With the e-version of this paper, extensive Supplementary Materials provide permanent access to data sets that are basic to our conclusions. These materials include detailed records of the specimens examined and of the more than 1300 recorded songs that were analyzed. Digitized versions of more than 450 of the recordings are archived in Cornell's Macaulay Library of Natural Sounds.
Journal of Orthoptera Research 07/2014; 23(1):1-38. DOI:10.1665/034.023.0102
[Show abstract][Hide abstract] ABSTRACT: Criteria for establishing water quality standards that are protective for 95% of the native species are generally based upon laboratory toxicity tests. These tests utilize common model organisms that have established test methods. However, for invertebrates these species represent mostly the zooplankton community and are not inclusive of all taxa. In order to examine a potential under-representation in emerging aquatic invertebrates the US Environmental Protection Agency has cultured a parthenogenetic mayfly, Centroptilum triangulifer (Ephemeroptera: Baetidae). This study established a 48h acute and a 14-day short-term chronic testing procedure for C. triangulifer and compared its sensitivity to two model invertebrates, Ceriodaphnia dubia and Daphnia magna. Toxicity tests were conducted to determine mortality and growth effects using standard reference toxicants: NaCl, KCl and CuSO4. In 48-h acute tests, the average LC50 for the mayfly was 659mgL(-1) NaCl, 1957mgL(-1) KCl, and 11μgL(-1) CuSO4. IC25 values, using dry weight as the endpoint, were 228mgL(-1) NaCl, 356mgL(-1) KCl and 5μgL(-1) CuSO4. C. triangulifer was the most sensitive species in NaCl acute and chronic growth tests. At KCl concentrations tested, C. triangulifer was less sensitive for acute tests but was equally or more sensitive than C. dubia and D. magna for growth measurements. This study determined C. triangulifer has great potential and benefits for use in ecotoxicological studies.
[Show abstract][Hide abstract] ABSTRACT: Development of methods for assessing exposure and effects of waterborne toxicants on stream invertebrate species is important to elucidate environmentally relevant information. Current protocols for freshwater invertebrate toxicity testing almost exclusively utilize cladocerans, amphipods or chironomids rather than the more typical aquatic insect taxa found in lotic systems. Centroptilum triangulifer is a parthenogenetic mayfly occurring in depositional habitats of streams and rivers of the Eastern U.S. and Canada. C. triangulifer is an ideal stream insect for toxicity testing under field and laboratory conditions because of its short life cycle, parthenogenetic mode of reproduction, and it represents a group considered sensitive to environmental stressors. In this study, a colony of C. triangulifer was reared using a defined diet of three diatoms, Mayamaea atomus var. permitis, Nitzschia cf. pusilla, and Achnanthidium minutissimum. Percent survival (⩾80%), fecundity measurements (⩾1000 eggs) and pre-egg laying weights were used as indicators of overall colony health and fitness in our laboratory water (Lab-line) and in Moderately Hard Reconstituted Water (MHRW). Lab-line reared C. triangulifer had average survival rate of 92.69% for eleven generations and 82.99% over thirteen generations. MHRW reared C. triangulifer had an average survival rate of 80.65% for four generations and three generations of fecundities greater than 1000 eggs per individual. Pre-egg laying weight and fecundity were highly correlated and a best-fit model equation was derived to estimate egg counts for future generations. Establishment of this culturing protocol provides a more ecologically relevant species for toxicity testing and aids in further stressor identification for stream bioassessments.
[Show abstract][Hide abstract] ABSTRACT: Little is known about the bioaccumulation dynamics, biotransformation processes, or subsequent toxicity to consumers of dissolved selenite (SeO3) versus selenate (SeO4) uptake into aquatic primary producer communities. To address these data gaps we examined SeO3 and SeO4 bioconcentration into complex freshwater periphyton communities under static and static-renewal conditions. Further, we explored periphyton biotransformation of Se species using X-ray absorption near edge structure (XANES) spectroscopy analysis and changes in the periphyton associated microbial consortium using denaturing gradient gel electrophoresis (DGGE). Last, we fed differentially treated periphyton to the mayfly Centroptilum triangulifer in full life cycle exposures to assess toxicity. Selenite exposed periphyton readily bioconcentrated Se while, in contrast, initial periphyton uptake of SeO4 was negligible, but over time periphyton [Se] increased steadily in conjunction with the formation of dissolved SeO3. XANES analyses revealed that both SeO3 and SeO4 treated periphyton biotransformed Se similarly with speciation dominated by organo-selenide (~61%). Mayfly survival, secondary production, and time to emergence were similar in both SeO3 and SeO4 treated periphyton exposures with significant adverse effects at 12.8 µg g-1 ((d.w.) secondary production) and 36 µg g-1 ((d.w.) survival and development time). Overall, dissolved selenium speciation, residence time, and organisms at the base of aquatic food webs appear to be the principal determinants of Se bioaccumulation and toxicity.
[Show abstract][Hide abstract] ABSTRACT: Cyrtoxipha gundlachi and Orocharis gryllodes are two common, well-studied Florida crickets whose scientific names are in doubt. We determine that C. gundlachi Saussure (1874) may retain its name and designate a neotype to stabilize that interpretation. We find that Cyrtoxipha orientalis Desutter-Grandcolas (2003) is a valid species rather than a junior synonym of Cyrtoxipha gundlachi sensu Otte & Perez-Gelabert (2009) and that the Jamaican species C. clarki Otte & Perez-Gelabert (2009) is a close relative of C. gundlachi. Finally, we determine that the Florida species formerly known as O. gryllodes (Pallas 1772) is now Antillicharis oriobates Otte & Perez-Gelabert (2009). Cyrtoxipha gundlachi y Orocharis gryllodes son dos grillos de la Florida comunes y bien estudiados cuyos nombres científicos están en duda. Nosotros determinamos que C. gundlachi Saussure (1874) puede conservar su nombre y aqui designamos un neotipo para estabilizar esa interpretation. Encontramos que Cyrtoxipha orientalis DeSutter-Grandcolas (2003) es una especie válida y no un sinónimo menor de Cyrtoxipha gundlachi sensu Otte & Pérez-Gelabert (2009) y que la especies de Jamaica, C. clarki Otte & Pérez-Gelabert (2009) es un pariente cercano de C. gundlachi. Por último, se determina que la especie de la Florida antes conocido como O. gryllodes (Pallas 1772) es ahora Antillicharis oriobates Otte & Pérez-Gelabert (2009).
[Show abstract][Hide abstract] ABSTRACT: Diet is often the predominant route of trace metal exposure in aquatic insects. In freshwater ecosystems, periphyton serves as a primary source of food to many aquatic insects and is a major sink for trace metals. We investigated the bioconcentration of the essential metal Zn by periphyton using (65)Zn as a radiotracer. At relatively low dissolved concentrations (2-20 μg L(-1)), non steady state Zn bioconcentration by periphyton averaged 6,099 ± 2,430-fold, with much of the variability determined by loading regime (number of renewals and duration of exposures). Labeled periphyton was used as a food source for dietary accumulation studies with the mayfly Centroptilum triangulifer. After 29 days, larvae concentrated Zn 19-, 16- and 17-fold relative to dietary Zn concentrations of 8.1, 43.2 and 82.3 μg g(-1) (dry weight), respectively. Adults from that same cohort only concentrated Zn 8-, 3- and 3- fold relative to those same dietary concentrations, revealing that mayflies lose significant Zn prior to reaching adulthood. Anecdotal evidence suggests that this loss occurs prior to emergence to the subimago, as negligible Zn was found in the subimago to imago exuvium. Across a range of adult tissue concentrations, maternal transfer consistently averaged 26.7 %. Uptake (k(u), 0.26 L g(-1 )d(-1)) and efflux rate constants (k(e), 0.001-0.007 d(-1)) were measured and assimilation efficiencies from dietary Zn concentrations of 4.9 and 59.7 μg Zn g(-1) were estimated to be 88 ± 4 % and 64 ± 15 %, respectively. Both life cycle and biodynamic modeling approaches point towards diet being the primary route of Zn bioaccumulation in this mayfly.
[Show abstract][Hide abstract] ABSTRACT: Selenium effects in nature are mediated by the relatively large bioconcentration of aqueous Se by primary producers and smaller, yet critical, dietary transfers to primary consumers. These basal processes are then propagated through food webs to higher trophic levels. Here we quantified the movement of dissolved Se (as selenite) to periphyton, and used the resultant periphyton as a food source for conducting full life-cycle dietary Se exposures to the mayfly Centroptilum triangulifer. Periphyton bioconcentrated Se ~2,200-fold from solution in a log-linear fashion over dissolved Se concentrations ranging from 1.1 to 23.1 μg L(-1). We examined the influence of two feeding ration levels (1x and 2x) on trophic transfer, tissue Se concentrations, maternal transfer, and functional endpoints of mayfly performance. Mayflies fed a lesser ration (1x) displayed greater trophic transfer factors (mean TTF, 2.8 ± 0.4) than mayflies fed 2x rations (mean TTF, 1.1 ± 0.3). In 1x exposures, mayflies exhibited significant (p < 0.05) reductions in survivorship and total body mass at dietary [Se] ≥ 11.9 μg g(-1), reduced total fecundity at ≥ 4.2 μg g(-1), and delayed development at ≥ 27.2 μg g(-1). Mayflies fed a greater ration (2x) displayed reduced tissue Se concentrations (apparently via growth dilution) relative to 1x mayflies, with no significant effects on performance. These results suggest that the influence of Se on mayfly performance in nature may be tied to food resource availability and quality. Furthermore, nutritional status is an important consideration when applying laboratory derived estimates of toxicity to risk assessments for wild populations.
[Show abstract][Hide abstract] ABSTRACT: Mayflies (Ephemeroptera) are important to the food web of most stream, river, and lake ecosystems and are critical to water-quality monitoring programs. They are widespread and ancient (predate dinosaurs) and have primitive reproductive systems and the shortest adult life spans of all insects. Here we formulate and test the hypothesis that facultative parthenogenesis occurs as a widespread adaptation in most, if not all, mayflies. A rare form of reproduction, facultative parthenogenesis combines the short-term advantages of parthenogenesis, which doubles reproductive output, with the long-term advantages of genetic variation associated with sex. For 7 species of bisexual mayflies, we show that their eggs hatched whether fertilized or not and that unfertilized eggs took longer to develop and hatch. However, once hatched, larvae produced via parthenogenesis grew and developed to the adult in a manner similar to that of larvae produced sexually. In addition, for all study species, female adults produced parthenogenetically were diploid and could reproduce either sexually (producing males and females equally) or parthenogenetically (producing mostly females and some males). Males produced parthenogenetically were viable and occurred either as 1st generation (F1) offspring or as offspring of F1 gynandromorphs (intersex individuals). Last, we show that parthenogenetic descendants lose ~10 to 22% of their genetic variation as a result of each parthenogenetic generation. We use these findings and observations and other published data to support the hypothesis that most, if not all, mayflies are facultatively parthenogenetic. We propose that this ability increases mayfly reproductive success by giving eggs from unmated or incompletely fertilized females a 2nd chance. We then formulate 3 additional hypotheses: 1) parthenogenetic development of mayfly eggs proceeds automatically soon after emergence but can be and normally is preempted by fertilization, and that this mechanism both helps to compensate for and is enabled by the peculiarities of life history and primitive reproductive biology in this ancient group; 2) that facultative parthenogenesis enhances mayfly dispersal and gene flow because it enables virgin females to transfer genes within and among catchments and to form bisexual populations in new habitat; and 3) that mayflies remain bisexual despite being able to reproduce without males because of lost genetic variation associated with the parthenogenetic process.
Journal of the North American Benthological Society 12/2010; 29(4):1258-1266. DOI:10.1899/10-015.1 · 2.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In 2006, the Stroud Water Research Center conducted inventories of stream macroinvertebrates in the Peninsula de Osa in Costa Rica and the Madre de Dios watershed in eastern Peru. Both areas have extensive lowland tropical rainforests under threat from road development, tourism, poaching and gold mining. The mayfly communities of the two regions were substantially different in family relative abundances. In Osa the mayfly community was more or less evenly divided among Baetidae, Leptohyphidae, and Leptophlebiidae. In streams where one group was clearly dominant, this was most often Leptohyphidae. By contrast, in the Madre de Dios watershed Leptophlebiidae was often 75% or more of the mayfly fauna while Leptohyphidae was 20% or less. In both Osa and Madre de Dios, EPT indices were calculated for impacted streams and relatively undisturbed streams. However, physical characteristics such as stream size and substrate diversity were often a better predictor of community composition than human activity.
[Show abstract][Hide abstract] ABSTRACT: Selenium contamination in aquatic ecosystems provides management challenges because bioaccumulation in animals is largely a function of dietary exposure, whereas regulatory entities have traditionally focused on direct water to organism interactions. Selenium is known to be readily absorbed by primary producers and can potentially biomagnify in food webs and elicit adverse effects in higher trophic levels. However, selenium bioaccumulation in the invertebrate prey of many predatory animals is poorly understood. Here, we used 75Se (as selenite) as a radiotracer to characterize Se bioaccumulation into natural periphyton biofilms and subsequent dietary and maternal transfer in the mayfly, Centroptilum triangulifer, in a life-cycle assay. On average periphyton biofilms bioconcentrated selenium 1113 (+/-430)-fold following 7-9 days of exposure to a range of environmentally relevant dissolved concentrations (2.4-13.9 microg L(-1)). Mayflies grown to adulthood on these diets further biomagnified Se with trophic transfer factors averaging 22 (+/-0.4)-fold in postpartum maternal tissues. Adults then transferred 46.5 (+/-8.8)% of their body burdens to eggs with an observed reduction in fecundity for mayflies fed on diets greater than approximately 11 microg g(-1). These results suggest that at environmentally feasible dietary Se concentrations insects are potentially affected by Se exposure, and that the current presumption that insects are simply conduits of Se to higher trophic levels is inaccurate.
[Show abstract][Hide abstract] ABSTRACT: In streams, periphyton biofilms are important sinks for trace metals such as cadmium and are primary food sources of many invertebrate consumers. To study Cd trophic transfer, we produced differentially contaminated diets by exposing natural periphyton to environmentally relevant dissolved Cd ranging from 0 to 10 microg L(-1) for 6-7 days using a radiotracer approach. On average, periphyton grown during three different seasons bioconcentrated Cd similarly--approximately 1315 (+/-442) -fold above dissolved concentrations. However, mayfly larvae (Centroptilum triangulifer) raised on these differentially contaminated diets (first instar through adulthood) had significantly higher trophic transfer factors from periphyton grown in Aug and Nov 2008 (4.30 +/- 1.55) than from periphyton grown in Jan 2009 (0.85 +/- 0.21). This Cd bioaccumulation difference is only partially explained by apparent food quality and subsequent growth differences. Taken together, these results suggest that primary producers at the base of food webs drive metal bioaccumulation by invertebrate grazers.
[Show abstract][Hide abstract] ABSTRACT: We compared genetic lineages in the mayfly genus Ephemerella (Ephemeroptera:Ephemerellidae) identified from mitochondrial DNA (mtDNA) to current taxonomy in 9 morphological taxa, including 2 geographically widespread species, Ephemerella invaria ( = E. inconstans, E. rotunda, E. floripara) and Ephemerella dorothea ( = E. infrequens). Maximum likelihood and parsimony analyses of the mtDNA sequences placed E. inconstans and E. invaria in a well-supported clade; however, mean Kimura 2-parameter genetic distance between the lineages was high (5.2%) relative to distance within lineages (1.3%). The phylogenetic relationships of synonyms E. rotunda and E. floripara were not resolved, but estimates of mean genetic distance to E. invaria were high for both (8.5% and 11.6%, respectively). Populations of E. dorothea were grouped in 2 well-supported clades (12.9% mean divergence) that did not include the synonym E. infrequens (20.9% mean divergence, based on a single sample). A large genetic distance (18.6%) also was found between eastern and western populations of Ephemerella excrucians. Western samples of Ephemerella aurivillii were so genetically distant from all other lineages (32.2%) that doubt about its congeneric status is raised. mtDNA data have been useful for identifying genetic lineages in Ephemerella, but our results do not support use of cytochrome oxidase I (COI) as a DNA barcode to identify species in this genus because we also found evidence of incomplete mtDNA lineage sorting in this gene. Use of the barcoding gene rediscovered some old taxonomic problems in Ephemerella, a result that emphasizes the importance of completing empirical systematic description of species before using single-character systems for identification.
Journal of the North American Benthological Society 06/2009; 28(3-3):584-595. DOI:10.1899/08-150.1 · 2.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We examined Hg(II) bioaccumulation and compartmentalization patterns in conjunction with antioxidant responses in four aquatic insect species: two caddisflies (Chimarra sp. and Hydropsyche betteni) and two mayflies (Maccaffertium modestum and Isonychia sp). Total antioxidant capabilities differed among unexposed larvae, with both caddisfly species exhibiting elevated antioxidant activities relative to the mayflies. We were able to account for these differences by examining the constitutive activities of catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), and superoxide dismutase (SOD), in the four species. We also examined levels of reduced and oxidized glutathione and cysteine in the insects. Glutathione peroxidase and SOD were the most responsive to Hg exposure, with GPx catalytic activity increasing between 50 and 310%. Superoxide dismutase activity decreased between 35 and 50%. This SOD suppression was shown to be dose-dependent in both caddisflies, butthe strength of this suppression did not appear to be related to rates of uptake. Surprisingly, little Hg (<10%) was found in the heat-stable cytosolic protein subcellular compartment in each of the four species, suggesting that Hg was not well detoxified. By combining bioaccumulation studies with other physiological measures, we can begin to better understand the consequences of trace metal pollutants in nature.
[Show abstract][Hide abstract] ABSTRACT: For many years the Drunella lata complex of eastern North America consisted of 4 recognized species: 3 described from the Northeast, Drunella lata (Morgan), Drunella cornuta (Morgan), and Drunella cornutella (McDunnough), and 1, Drunella longicornis (Traver), from the southern Appalachian Mountains region. Recently, all 4 were synonymized to a single species (D. lata [Morgan], by priority) because morphological variation was perceived to be continuous and historical characterizations of species were viewed as arbitrary. We used genetic, morphometric, and life-history data to reevaluate D. lata, D. cornuta, and D. cornutella in northeastern North America, where all 3 morphotypes coexist in certain catchments and often in the same reach of stream. Pairwise genetic comparisons of coexisting morphotypes revealed fixed allelic differences at 6 to 10 of 19 allozyme loci, showing reproductive isolation among D. cornuta, D. cornutella, and D. lata even within the same reach of stream. Morphometric studies confirmed their distinction by uncovering significant differences in a suite of characters, some with nonoverlapping ranges (i.e., diagnostic). The 3 taxa also were shown to be segregated ecologically by consistent differences in seasonality, thermal requirements, and spatial distribution. We conclude that D. cornuta, D. cornutella, and D. lata are all worthy of full species status, and so reinstate D. cornuta and D. cornutella. Diagnostic descriptions are provided and existing keys emended.
Journal of the North American Benthological Society 09/2008; 27(3):647-663. DOI:10.1899/08-026.1 · 2.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Eurylophella oviruptis new species is described and illustrated from female larvae and reared subimagos and imagos collected from swamp streams in North Carolina, USA. Several key morphological characters in the larva place this new species in the Eurylophella temporalis group. Genetic comparisons with other eastern North American Eurylophella revealed a fixation of alleles unique to E. oviruptis at 4 of 19 allozyme loci. Eurylophella oviruptis appears to be obligately parthenogenetic because no males were observed in the field or laboratory and eggs taken from subimagos and imagos hatched parthenogenetically (mean hatch rate ¼ 79%). Abdomens of 60% of subimagos reared in the laboratory burst along the ecdysial line of the first 3 tergites immediately after transformation to the subimago at the water surface. Abdominal bursting ruptured the oviducts, released most of the eggs into the water, and left the subimago trapped on the water surface with a large, inflated midgut protruding from the split in the tergites. Subimagos that did not burst (40%) flew from the water surface, molted to the imago on the 2nd day following emergence, and then, without having mated, extruded a ball of eggs that was released into the water. Dissections of E. oviruptis and 5 other species of mayflies showed that inflation of the mayfly gut normally occurs at 3 stages: emerging larvae inflate prior to and during the molt to the subimago, subimagos (particularly males) inflate further at the imaginal molt, and female imagos inflate even further at oviposition. Gastrointestinal inflation in mayflies maintains full abdominal distention that might facilitate flight. Abdominal bursting in E. oviruptis subimagos appears to be the result of gut inflation well beyond the amount normally associated with this stage. The evolutionary significance (predation, dispersal, demographics) of oviposition by abdominal bursting is discussed.
Journal of the North American Benthological Society 06/2008; 27(2):269-279. DOI:10.1899/07-128.1 · 2.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Allozymes were used to examine population genetic structure and species boundaries in the clonal, obligately parthenogenetic Centroptilum triangulifer and its sexual sister species Centroptilum alamance from 3 sites in Pennsylvania and 1 site in North Carolina, USA. Genotype frequencies in field populations of C. triangulifer showed numerous departures from Hardy-Weinberg expectations (mostly heterozygote excesses) and significant linkage disequilibrium at most testable locus combinations, as expected for a clonal parthenogen. A total of 51 distinct clones of C. triangulifer was identified, some of which were found at multiple sites (separated by .700 km in one case). Each stream contained from 7 to 25 clones and clonal frequencies at a given site varied greatly over time. Allelic patterns in laboratory hybrids suggest that parthenogenesis in C. triangulifer is diploid and automictic, and that crossing over is suppressed. In contrast, C. alamance populations had only a few Hardy-Weinberg departures (all heterzygote deficiences) and little or no linkage disequilibrium. No published work provides characters to distinguish the 2 species, but our data support retention of specific status for C. triangulifer and C. alamance because: 1) consistent, fixed allelic differences were found over a broad geographic area (.700 km) with no evidence of introgression despite co-occurrence (sympatry) in the same stream, 2) laboratory hybridization experiments demonstrated the existence of postzygotic barriers to gene flow between the species, and 3) measures of both interspecific and intraspecific genetic similarity were comparable to those found between other mayfly species. Phylogenetic analysis of the genetic data suggests speciation preceded the transition to obligate parthenogenetic reproduction in C. triangulifer. Morphological examination of genetically identified specimens enabled us to describe subtle but consistent differences that can be used to distinguish the species. Thus, what initially appeared to be single populations with skewed sex ratios (7, 11, and 24% male) at 3 of our study sites was, in fact, 2 populations at each site—1 exclusively female (C. triangulifer) and the other a normal, sexual (1:1 sex ratio) population (C. alamance). A similar approach, combining detailed genetic and breeding experiments with close morphological study, could help resolve taxonomic problems in some of the numerous other bisexual/parthenogenetic mayfly taxa.
Journal of the North American Benthological Society 06/2006; 25(2):417-429. DOI:10.1899/0887-3593(2006)25[417:TAGOTP]2.0.CO;2 · 2.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Life history characteristics of the stream mayfly Euthyplocia hecuba (Hagen) (Polymitarcyidae:Euthyplociinae) were studied over a 4-yr period in two tropical streams (Río Tempisquito and Quebrada Marilin) draining primary evergreen forest in northern Costa Rica. Larvae burrow in the substratum of the stream, living under small to large cobbles that are firmly embedded in the stream bottom. Euthyplocia hecuba is sexually dimorphic and one of the largest mayflies of Central America, with maximum larval size of 149 mg (dry mass) for females and 35 mg for males. Mature female and male larvae are about 40% larger in Q. Marilin relative to R. Tempisquito. Subimagoes emerge about 1 h before dawn (∼0400 h); the molt to the imago (or true adult stage) occurs ∼20 min later. Adult emergence and reproduction occurs mainly between June and November. Females mate and then oviposit in riffle areas just before dawn, with the time period gradually changing from 0446 and 0507 h in June to 0508 and 0529 h in October. We found that size of adult males and females gradually declined during the emergence period. Fecundity averaged 984 in October (range 364-2851), with eggs being very large for a mayfly (0.46 × 0.4 mm; 0.017 mg dry mass). The proportion of adult biomass allocated to eggs (reproductive effort) averaged 0.51 but varied according to female size. Median egg development time was 113, 55, and 31 d at 15, 20, and 25°C. The hatch success of eggs was >90% at 15 and 20°C, only 68% at 25°C, and 0% at 10 and 30°C. First instar larvae are relatively large for a mayfly, having a head width of 0.11 mm and a body length of 1.30 mm. Seasonal changes in larval size distribution suggest that larval development takes ∼22 mo to complete and may involve a developmental quiescence or diapause during the first year. A 2-yr life history appears to be the most parsimonious hypothesis given a 2-mo egg development time, the occurrence of two size cohorts of larvae throughout most of the year, and the temporal pattern of maximum and average larval sizes over the course of the sampling period. Our data suggest that seasonality in the developmental dynamics of larvae underlies both the seasonal emergence and decline in dry mass of both adult males and females during the emergence period. The data provide the first evidence for semivoltinism in a tropical mayfly.
Journal of the North American Benthological Society 03/1995; 14(1):131. DOI:10.2307/1467729 · 2.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mayflies transferred similar to 70% of their chlordane load into eggs along with 44-52% of their lipids. Lipid pools comprising adult tissues and their eggs were not at equilibrium in terms of chlordane concentration, with the eggs containing several times that of the mothers' adult tissues. However, chlordane fingerprints in eggs and adults were similar in terms of distribution of chlordane components and metabolites. Mayflies fed pretreated algae were indistinguishable from those exposed to chlordane added to their water. Mayflies transformed the technical chlordane into a signature dominated by the nonachloro component trans-nonachlor and the two metabolites heptachlor epoxide and oxychlordane. This was anomalous in comparison to organisms of similar trophic levels and more like the level of transformation measured in higher organisms, such as the porpoise and humans. Disequilibrium between lipid tissues of mayflies and their eggs highlights the limitations of modeling contaminant impact by measuring only whole body contaminant burdens.