Larval Biology Research Articles

Description of Atherinella brasiliensis (Quoy & Gaimard, 1825) (Atheriniformes: Atherinopsidae) larvae from the Jaguaribe River estuary, Itamaracá island, Northeastern Brazil

The present study describes the external morphology and morphometry of the initial development of Atherinella brasiliensis, and contributes toward broadening knowledge on its biology. A total of 88 larvae and 14 juveniles were used to characterize the morphological development and analyze body proportions. Fish with standard lengths (SL) from 1.4 to 77 mm were used in the study. Larvae hatch at an average of 1.4 mm SL. In the preflexion stage, the larval body is enveloped by a finfold, which begins behind the head. Pectoral fins are the first to be formed and preflexion larvae have four characteristic dendritic chromatophores on the head. The flexion stage begins at an average of 4.4 mm SL; dorsal and anal fins already exhibit pterygiophores and a terminal, somewhat up-turned mouth. At 6.8 mm SL, the flexion stage ends. In the postflexion stage, larvae present greater ossification of the dorsal and anal fin rays, exhibit pelvic fin buds and a darkening of lateral pigmentation. At an average of 8.8 mm SL, head pigmentation intensifies and pelvic fins exhibit conspicuous ossifying rays. Larvae at 11.8 mm SL have all fins formed; the second dorsal fin is the last to be formed at an insertion point posterior to the anal fin. The juvenile period begins at approximately 12 mm SL. At this stage, A. brasiliensis has an anal fin located at the median portion of the body and the posterior end of pectorals surpasses the origin of pelvic fins, which are located at the midpoint between the pectoral and anal fins. Scales are present on the dorsal-lateral region behind the head. The morphological features of A. brasiliensis herein described allow an adequate identification of its larvae and differentiate them from hemiramphid and other atheriniform larvae, thus broadening knowledge on the larval biology of the species.

THE MOLECULAR GENETICS OF LARVAL MOSQUITO BIOLOGY: A PATH TO NEW STRATEGIES FOR CONTROL

In the last 20 years, genetics, molecular genetics and genomics have advanced tremendously and supplied numerous new technical approaches and possibilities to biological control strategies. The tools of molecular genetics and genomics are now being applied by numerous groups to questions that are directly relevant to the biological control of mosquito populations. As the world-wide effort to control disease vector insects such as mosquitoes seems to be dropping behind the innate capacity of mosquitoes to adapt to extrinsic pressures such as pesticide exposure, a need for new avenues for development of controls has become paramount. Many view molecular biology as the likely source of truly novel control strategies. It is beyond the scope of this manuscript to review the entire range of investigations utilizing molecular methodologies toward mosquito control. Instead this chapter will touch on a few very important areas of research that are currently in progress around the world. Then it will discuss some of the specific efforts that our lab has undertaken with regard to the molecular analyses of larval mosquito biology and that approach as a path to novel control strategies.

A New Species of Xylotrechus(Coleoptera: Cerambycidae: Cerambycinae: Clytini) from Southern California, U.S.A

Abstract Xylotrechus hovorei, new species, is described from southern California, and its host plant and larval biology are characterized. Separation from closely related species of Xylotrechus is discussed.

Stability of Formulated Diets and Feeding Response of Stage I Western Spiny Lobster, Panulirus cygnus, Phyllosomata

Abstract This study is a preliminary assessment of suitable binders and formats of potential formulated diets for hatchery growout of early‐stage western spiny lobster, Panulirus cygnus, phyllosomata. Six dry meal (each bound with a different binder) and three gelatinous (all bound using gelatine) diets were tested for stability in water over increasing periods of time (4, 8, and 12 h), and the feeding response to each was observed by video analysis. The gelatinous krill diet appears most suited to the larval feeding biology of P. cygnus phyllosomata as it elicited a heightened feeding response immediately following immersion, was most stable in water up to 4 h, and did not foul the maxillae during ingestion. The dry meal diets were not as stable in water and contributed to excessive fouling of the maxillae during ingestion. Of the dry meal diets, the most suitable was bound with 5% k‐carrageenan, presumably because of high moisture content and softer texture.

RAPID ADAPTATION TO A NOVEL HOST IN A SEED BEETLE (CALLOSOBRUCHUS MACULATUS): THE ROLE OF SEXUAL SELECTION

Rapid diversification is common among herbivorous insects and is often the result of host shifts, leading to the exploitation of novel food sources. This, in turn, is associated with adaptive evolution of female oviposition behavior and larval feeding biology. Although natural selection is the typical driver of such adaptation, the role of sexual selection is less clear. In theory, sexual selection can either accelerate or impede adaptation. To assess the independent effects of natural and sexual selection on the rate of adaptation, we performed a laboratory natural selection experiment in a herbivorous bruchid beetle (Callosobruchus maculatus). We established replicated selection lines where we varied natural (food type) and sexual (mating system) selection in a 2 x 2 orthogonal design, and propagated our lines for 35 generations. In half of the lines, we induced a host shift whereas the other half was kept on the ancestral host. We experimentally enforced monogamy in half of the lines, whereas the other half remained polygamous. The beetles rapidly adapted to the novel host, which primarily involved increased host acceptance by females and an accelerated rate of larval development. We also found that our mating system treatment affected the rate of adaptation, but that this effect was contingent upon food type. As beetles adapted to the novel host, sexual selection reinforced natural selection whereas populations residing close to their adaptive peak (i.e., those using their ancestral host) exhibited higher fitness in the absence of sexual selection. We discuss our findings in light of current sexual selection theory and suggest that the net evolutionary effect of reproductive competition may critically depend on natural selection. Sexual selection may commonly accelerate adaptation under directional natural selection whereas sexual selection, and the associated load brought by sexual conflict, may tend to depress population fitness under stabilizing natural selection.

Life history of gnathiid isopods-current knowledge and future directions

Gnathiidae is a family of Isopoda, showing a distinct morphology and ecology. Species in the family have ten walking legs compared to 14 for isopods in general. The life cycle of the Gnathiidae is biphasic including a fish-par- asitic larval phase and a non-feeding adult phase, whereas most other isopods have a monophasic life cycle with direct- developing young similar to adults in morphology and ecology. Although the ecological information on gnathiids has been described fragmentally, studies on the life cycles and population biology have increased dramatically since the 1980's. Larval biology including the host species, emergence pattern and predation risks during parasitism have also been studied from the view of fish disease and symbiotic interactions among fishes. Some authors reported the utiliza- tion patterns of benthic substrata and harem formation of adults therein. However, the ecological knowledge of gnathi- ids is based on a limited number of species of which the benthic habitats are known. Studies rarely identify larvae be- cause of the lack, or insufficiency, of the taxonomic description of larvae of most species. The difficulty in identifying larvae has prevented detailed examination of ectoparasitic behaviour. Furthermore, gnathiid larvae emerging from the benthos or attaching to hosts have been investigated separately from benthic individuals. More efforts on taxonomy and the classification of larvae are necessary to elucidate the larval ecology and the integration of larval and adult biology.

REDESCRIPTION OF THE TADPOLE OF CHACOPHRYS PIEROTTII (VELLARD, 1948) (ANURA, CERATOPHRYIDAE)

Abstract A detailed redescription of the larval morphology of the ceratophryid frog Chacophrys pierottii is presented with an account of the pattern of lateral-line organs and comments on larval biology. Variation in the nasal appendix, a unique feature of Chacophrys tadpoles, is described. Comparisons are made with larvae of two closely related genera, Ceratophrys and Lepidobatrachus. In contrast to members of these genera, which have highly modified carnivorous larvae, the larvae of Chacophrys pierottii resemble typical Type IV tadpoles. However, the larvae of all ceratophryid genera possess uninterrupted marginal papillae surrounding the oral disc.

Sponge Systematics by Starfish: Predators Distinguish Cryptic Sympatric Species of Caribbean Fire Sponges,Tedania ignisandTedania klausin. sp. (Demospongiae, Poecilosclerida)

Tedania ignis (Duchassaing and Michelotti, 1864), the fire sponge, is common throughout the tropical western Atlantic, and is a popular species for studies of ecology, larval biology, and chemistry. T. ignis is readily consumed by seagrass-dwelling starfish, and so finding sponges similar to this species in a seagrass meadow provoked closer scrutiny. A variety of ecological, morphological, and molecular traits consistently and unambiguously distinguish T. ignis from a cryptic sympatric congener, here described as Tedania klausi, n. sp. Starfish that consume T. ignis reject T. klausi, and angelfish consume T. klausi less quickly. In Belize, T. ignis individuals transplanted to a seagrass meadow inhabited by T. klausi were consumed by starfish, and individuals of T. klausi transplanted to a mangrove-lined creek in which T. ignis flourishes, died. In Panama, many individuals of T. klausi were diseased in May 2004, while adjacent individuals of T. ignis were unaffected. Spicule types are the same in the two forms, and sizes overlap; but within individuals, the relative sizes of styles and tylotes differ in a pattern that distinguishes the two forms. Comparison of DNA sequences for mitochondrial cytochrome c oxidase subunit I (COI) revealed that 8 single nucleotide mutations consistently differ between the two forms regardless of habitat (seagrass vs. mangrove) and geographically separated sites (Belize vs. Panama).

Reproductive and larval biology of the sub-Antarctic hermit crab Pagurus comptus reared in the laboratory

Fecundity, hatching rhythm, and the planktotrophic larval development of the hermit crab Pagurus comptus from sub-Antarctic waters of the Beagle Channel (Tierra del Fuego) were studied under controlled laboratory conditions of temperature, light cycle, food supply, and salinity. Fecundity was low, ranging from 134 to 848 eggs per female (cephalotoraxic shield length, SL, 2.3–5.0 mm). Hatching observed in the laboratory ranged from 6 to 30 d. The larval development was studied in laboratory cultures fed with Artemia sp. nauplii and kept at constant 7.0±0.5°C. Larvae invariably passed through four zoeal instars and one megalopa stage. Mean durations of the zoeal stages I to IV were 14.3±1.8, 16.7±4.6, 23.2±6.5, 33.4±9.2 d, respectively. Combined with the 43.8±5.6 d recorded for the survived megalopae, we suggest that the complete larval development lasts about four months. Starved larvae, on average, survived for 22±8.1 d (maximum 38 d) by far exceeding the zoea I duration in fed larvae, but did not reach the moult to the zoea II stage. Unlike other sub-Antarctic decapods, which show a tendency towards abbreviated or endotrophic larval developments at high latitudes, hermit crabs, at their southernmost distributional limit on Earth, show an extended and fully planktotrophic larval development and thus need to synchronize larval release with short periods of high primary production.

The rule of Thorson-Rass: One or two independent phenomena?

Two investigators, G. Thorson in the example of invertebrates and T.S. Rass in the example of fishes, simultaneously documented an increase in the egg size of aquatic organisms with a decrease in water temperature. This pattern is related to two different phenomena, which are erroneously united into the well-known rule of Thorson-Rass. Thorson’s rule describes ecological processes linked to the change in larval biology and morphology that are caused by the natural selective pressure on different types of larval development. Rass’ rule describes physiological processes and manifests itself in comparisons within populations, between populations of the same species, and between closely related species, and it is not associated with the change of type of reproductive strategy or with the biology of early development stages. Thorson’s rule describes the relative abundance of both r-and K-strategists within an r-K-continuum, whereas Rass’ rule characterizes the relative position of both groups within the continuum.

Deep-sea Hydrothermal Vents: Ecology and Evolution

The discovery of deep-sea hydrothermal vents and their ecosystems is a monumental landmark in the history of Ocean Sciences. Deep-sea hydrothermal vents are scattered along the global mid-ocean ridges and back-arc basins. Under sea volcanic phenomena related to underlying magma activities along mid-ocean ridges generate extreme habitats for highly specialized communities of animals. Multidisciplinary research efforts during past three decades since the first discovery of hydrothermal vents along the Galapagos Rift in 1977 revealed fundamental components of physiology, ecology, and evolution of specialized vent communities of micro and macro fauna. Heterogeneous regional geological settings and tectonic plate history have been considered as important geophysical and evolutionary factors for current patterns of taxonomic composition and distribution of vent faunas among venting sites in the World Ocean basins. It was found that these communities are based on primary production of chemosynthetic bacteria which directly utilize reduced compounds, mostly <TEX>$H_2S$</TEX> and <TEX>$CH_4$</TEX>, mixed in vent fluids. Symbioses between these bacteria and their hosts, vent invertebrates, are foundation of the vent ecosystem. Gene flow and population genetic studies in parallel with larval biology began to unveil hidden dispersal barrier under deep sea as well as various dispersal characteristics cross taxa. Comparative molecular phylogenetics of vent animals revealed that vent faunas are closely related to those of cold-water seeps in general. In perspective additional interesting discoveries are anticipated particularly with further refined and expanded studies aided by new instrumental technologies.

Latitudinal and bathymetric trends in egg size variation: a new look at Thorson's and Rass's rules

AbstractThe inverse relationship between egg size in marine animals and water temperature was simultaneously described by two outstanding marine scientists: G. Thorson and T.S. Rass. This rule consists of two different phenomena. Thorson's rule describes ecological processes related to changes in larval biology and morphology that are caused by a selective pressure of natural selection on the different types of larval development. It belongs to the realm of macro‐evolution. Rass's rule describes physiological processes within populations and species, and between closely related species. This is not related to changes in reproductive strategy, and therefore belongs to the realm of micro‐evolution and to the early stages of macro‐evolution. Populations begin to produce larger eggs in colder environments because of phenotypic plasticity. Thorson's rule describes temperature‐dependent changes in the relative abundance of small‐ and large‐egged species, whereas Rass's rule describes a temperature‐dependent relative position of both groups within an adaptive range of reproductive strategies.

Contributions of larval biology to crustacean research: a review

Summary Many aquatic crustaceans pass through a complex life cycle comprising a benthic juvenile-adult and a pelagic larval phase. In the study of aquatic ecology, meroplanktonic larvae are therefore considered as principal components of benthic-pelagic coupling processes. As a consequence of radical transitions of life style, larvae differ from conspecific adults in their ecology, behaviour, nutrition, morphology, and physiology. Ontogenetic changes of these traits, as well as carry-over effects of larval condition on postmetamorphic fitness of benthic juveniles, are subjects of the interdisciplinary field of larval biology. Larval biology is thus not only an intrinsic part of lifehistory studies, but contributes essential information also to various other biological disciplines, including the broad area of crustacean research. For economically important species, it provides critical information for the development of aquaculture techniques or for the management of sustainable fisheries. Inferring from heritable ontogenetic patterns, comparative studies of larval morphology also aid the identification of phylogenetic relationships within and among higher taxa (“Evo-Devo” perspective). On the other hand, larval traits may be modified by environmental factors, which link larval ecology to developmental biology (“Eco-Devo” approach). Patterns of larval dispersal, mortality, and recruitment are crucial for the stability of benthic populations and communities. These aspects of “supply-side ecology” have also consequences for patterns of biogeographic distribution, population connectivity, genetic diversity, and the formation of metapopulations. In addition, the spread of introduced species in recipient regions may be explained or predicted through developmental and ecophysiological traits of their larvae. In evolutionary biology, knowledge of reproductive and developmental adaptations is crucial for the understanding of limnic and terrestrial invasions by originally marine crustaceans.

The species‐area relationship in the hoverfly (Diptera, Syrphidae) communities of forest fragments in southern France

The effect of forest fragmentation was studied in hoverfly communities of 54 isolated forests (0.14–171 ha) in south west France. The positive relationship between species richness and wood patch area was investigated by testing the three hypotheses usually put forward to explain it: 1) the sampling effect hypothesis, 2) the patch heterogeneity hypothesis, 3) the hypothesis of equilibrium between distance from other patch (colonisation) and surface area of the patch (extinction). The syrphid species were divided into 3 ecological groups, based on larval biology as summarized in the “Syrph the Net” database: non forest species, facultative forest species and forest species. A total of 3317 adults belonging to 100 species, were captured in the 86 Malaise traps. Eight species were non forest (N=16), 65 facultative forest (N=2803) and 27 forest species (N=498).Comparison of the slopes of the species‐area curves for species richness and species density per forest patch showed a strong sampling effect in the species‐area relationship. Wood patch heterogeneity increased with wood patch area and positively influenced hoverflies richness. Less isolated wood patches presented high richness of forest species and low richness of non forest species. Only forest species richness seemed to respond to the equilibrium between surface area and isolation. Depending on which hypothesis explained best the species‐area relationship, management recommendations to mitigate fragmentation effects were formulated at various spatial scales and for different stakeholders.

Larval biology, life cycle and habitat requirements ofMacromia splendens, revisited (Odonata: Macromiidae)

Abstract Information on larval biology of Macromia splendens was compiled and supplemented by hitherto unpublished data. Larvae inhabit mainly calm river stretches, sometimes artificial impoundments, and lentic margins of lotic sections. From the majority of records it is concluded that the larvae mainly dwell in sandy substrates in shallow water, which sometimes contains little leaf litter. Larvae occur in smaller numbers on substrates dominated by coarse detritus or on bedrock in deeper water. Larvae of M. splendens are able to burrow in sand, but such burrowing takes a long time, and sometimes parts of their body remain uncovered. Therefore, they are considered shallow burrowers. Based on head-width frequency distributions recorded at the Gardon de Mialet, southern France, the species is believed to require two years per generation.

Dispersal of an introduced larval cohort in a coastal lagoon

Patterns of larval dispersal influence the structure of marine biological communities, but many aspects of larval dispersal remain poorly understood. For example, much of our present understanding of larval dispersal is based on models that integrate aspects of physical oceanography and larval biology, but the predictions of those models are generally not tested because we lack the methodology for real-time larval tracking. In the present study, we used both modeled and measured data to track an introduced larval cohort essentially from fertilization to presumed settlement. Larvae of the hard clam Mercenaria were released into a labeled water parcel in the Banana River Lagoon, Florida, within 8.5 h of nursery production and then were tracked for the duration of their estimated 8-d pelagic life span. Comparisons of modeled versus measured larval distribution indicate that the fate of the larvae as predicted by a tracer model and by the concentration of coincidentally released sulfur hexafluoride (SF 6) did not agree with the fate of the larvae as predicted by the path of subsurface drifters and by a particle trajectory model. Thus, modeled predictions of larval dispersal must be interpreted with care. Additionally, one component of larval dispersal that was observed in the study but that was not accounted for in the model was the spread of larvae along the path of advection. That trail of larvae may have important consequences for patterns of recruitment and resultant community structure, but it is not considered in most treatments of larval dispersal.

Microtiter plate, optode respirometry, and inter-individual variance in metabolic rates among nauplii of Artemia sp.

Understanding the potential metabolic lifespan of a cohort of marine invertebrate embryos or larvae requires not just precise measurements of respiration rates, but also requires a large number of individual-level measurements to accurately describe the distribution of metabolic rate potentials within that cohort. To this end, we have developed a simple protocol for converting a 384-well microtiter plate into a 384-chamber, microrespirometer, optode using a plate-reading fluorometer for continuous, real-time data acquisition. We have ground-truthed this high-throughput technique using Artemia sp. nauplii at ~48 h post-hydration. In this paper we present >1000 separate respiration rate measurements on nauplii, providing a novel look at the distribution of metabolic rates within a cohort of larvae. At this high level of individual sampling, we have applied a Shan- non-Weaver information entropy statistic to describe the 'complexity' of these rate distributions and to show that the range of metabolic phenotypes expressed in a group of nauplii is responsive to the salinity in which they are rehydrated. Understanding the nature and mechanisms by which variations in metabolic rate intensities can be so large within a cohort and can be responsive to environmental parameters represents a real challenge in larval biology, which will require high-throughput method- ologies at both molecular and biochemical levels to decipher.

Larval and Pupal Descriptions of the Neotropical Choreutid Genera &lt;I&gt;Rhobonda&lt;/I&gt; Walker and &lt;I&gt;Zodia&lt;/I&gt; Heppner (Lepidoptera: Choreutidae)

Larvae and pupae of two Neotropical choreutids, Rhobonda gaurisana Walker and Zodia scintillana (Walker) (Lepidoptera: Choreutidae), are described. Photographs, drawings, and scanning electron micrographs are provided for both species, and observations on larval behavior and biology are reported. The larval head in both genera is reinterpreted as being semiprognathous. The D2 setae on A9 arise from a common middorsal pinaculum in Rhobonda, Zodia, and other choreutid genera. Previously, this character was regarded as one of the defining characters for the Tortricidae. The implications of its presence in choreutids are discussed. The variability of the arrangement of pupal dorsal spines between the Millieriinae and the other two subfamilies Brenthiinae and Choreutinae is so great that the inclusion of the Millieriinae with the Choreutidae is questioned.

Larval morphology and biology of oxycorynine weevils and the higher phylogeny of Belidae (Coleoptera, Curculionoidea)

Phylogenetic relationships among members of the family Belidae (Curculionoidea) were reconstructed through cladistic analysis using 58 characters and 17 terminals. The characters were from larval morphology (30), adult morphology (25) and biology regarding larval host‐plants and feeding habits (three). They were scored for exemplar taxa in 17 genera, representing different belid subfamilies and tribes, plus two outgroup taxa in Megalopodidae and Nemonychidae. The sampled genera included all those for which larval and adult information is available, and two known only from adults. New information on the larvae and biology of two oxycorynines is provided. These are the Chilean Oxycraspedus cribricollis, whose larvae live in decayed female strobili of the gymnosperm Araucaria araucana, and Hydnorobius hydnorae from Argentina, whose larvae, described and illustrated in the present paper, develop inside the flower and fruit bodies of Prosopanche americana (Hydnoraceae), a root‐parasitic angiosperm. The relationships proposed by the single optimal cladogram resulting from simultaneous analysis of all taxa and characters are recovered by one of three optimal cladograms based on the larval data set alone. The cladogram justifies a revised classification of Belidae in two sister subfamilies: Belinae (with tribes Pachyurini, Agnesiotidini and Belini) and Oxycoryninae (with tribes Oxycorynini and Aglycyderini). It summarizes larval and adult synapomorphies defining the family Belidae, subfamilies and tribes. Based on the phylogenetic tree, the evolution of biological traits is traced. Larval development in vegetative organs of conifers is ancestral in Belidae. A shift to reproductive structures characterizes the Oxycorynini, a habit which was conserved while several shifts to distantly related host‐plant groups occurred.

Fertilization, post-fertilization development and larval biology of the South African polychaete, Arenicola loveni loveni (Kinberg 1866)

Summary Larval development in the South African polychaete Arenicola loveni loveni is described, and the effects of seawater temperature on fertilization success, post-fertilization development and early post-settlement survivorship are experimentally determined. Fertilization success was significantly effected by seawater temperature, with maximum fertilization success measured in the range 15–18°C, which is close to the ambient temperature range at the time of natural spawning. Poor fertilization success and abnormal cleavage were observed at the low temperature treatment of 7°C and the high temperature treatment of 23°C. A. loveni loveni exhibits spiral cleavage typical of polychaetes and has a short lecithotrophic swimming trochophore larval stage of 4–5 days. High mortality was noted during the transitional periods from gastrula-trochophore and during the settlement process. Settlement occurs just 4–5 days post-fertilization and the postsettlement stage begins feeding 1 week post-fertilization. Temperatures in the range 16.5–23°C were found to have a significant effect on larval and post-larval survivorship and growth rate increased with temperature within this range. The effects of manipulating spawning date on subsequent offspring survival and development rates were also investigated. Advancing or delaying spawning time caused reduced development rates, and delaying spawning for 3 months was found to significantly reduce offspring survivorship.