Morphogenesis accompanying larval metamorphosis in Plakina trilopha (Porifera, Homoscleromorpha)

Morphological investigations of morphogenesis accompanying the metamorphosis of the cinctoblastula larva of poriferan Plakina trilopha (Homoscleromorpha) have been made. The larva possesses a distinct columnar epithelium which subdivides into three cellular areas: antero-lateral, postero-lateral, and posterior one. Characteristic morphological features of the cells in each area can be used as natural markers when tracing the fate of larval cells during metamorphosis. The ciliated epithelium of the larva is transformed directly into choanoderm and pinacoderm, without losing its organization. This transformation is a peculiar feature of the metamorphosis in Homoscleromorpha. Metamorphosis in P. trilopha is based on epithelial morphogenesis and includes the mechanisms of flattening of the exopinacoderm, evagination and invagination of larval epithelium in the course of the development of the rhagon aquiferous system. The flattening of larval cells during exopinacoderm formation in metamorphosing P. trilopha is a common change of cell shape during epithelial morphogenesis of this species. The separation of proximal fragments of cells has been observed here. This phenomenon, that we have called “cytoplasmic shedding”, appears to play an important role in the change of epithelial cell shape in P. trilopha. Mechanism of epithelial–mesenchymal transition, i.e., ingression of epithelial ciliated cells into the cavity of the metamorphosing larva of P. trilopha participates in mesohylar cell origin.     

Phenotypic plasticity, heterochrony and ontogenetic repatterning during juvenile development of divergent Arctic charr (Salvelinus alpinus)

Phenotypic plasticity is a developmental process that plays a role as a source of variation for evolution. Models of adaptive divergence make the prediction that increasing ecological specialization should be associated with lower levels of plasticity. We tested for differences in the magnitude, rate and trajectory of morphological plasticity in two lake populations of Arctic charr (Salvelinus alpinus) that exhibited variation in the degree of resource polymorphism. We reared offspring on diet treatments that mimicked benthic and pelagic prey. Offspring from the more divergent population had lower levels of morphological plasticity. Allometry influenced the rate of shape change over ontogeny, with differences in rate among ecomorphs being minimal when allometric variation was removed. However, plasticity in the spatial trajectory of development was extensive across ecomorphs, both with and without the inclusion of allometric variation, suggesting that different aspects of shape development can evolve independently.     

Phenotypic integration in the feeding system of the eastern diamondback rattlesnake (Crotalus adamanteus)

Selection can vary geographically across environments and temporally over the lifetime of an individual. Unlike geographic contexts, where different selective regimes can act on different alleles, age‐specific selection is constrained to act on the same genome by altering age‐specific expression. Snake venoms are exceptional traits for studying ontogeny because toxin expression variation directly changes the phenotype; relative amounts of venom components determine, in part, venom efficacy. Phenotypic integration is the dependent relationship between different traits that collectively produce a complex phenotype and, in venomous snakes, may include traits as diverse as venom, head shape and fang length. We examined the feeding system of the eastern diamondback rattlesnake (Crotalus adamanteus) across environments and over the lifetime of individuals and used a genotype–phenotype map approach, protein expression data and morphological data to demonstrate that: (i) ontogenetic effects explained more of the variation in toxin expression variation than geographic effects, (ii) both juveniles and adults varied geographically, (iii) toxin expression variation was a result of directional selection and (iv) different venom phenotypes covaried with morphological traits also associated with feeding in temporal (ontogenetic) and geographic (functional) contexts. These data are the first to demonstrate, to our knowledge, phenotypic integration between multiple morphological characters and a biochemical phenotype across populations and age classes. We identified copy number variation as the mechanism driving the difference in the venom phenotype associated with these morphological differences, and the parallel mitochondrial, venom and morphological divergence between northern and southern clades suggests that each clade may warrant classification as a separate evolutionarily significant unit.     

Presumptive environmental effects on body shape of Aplochiton zebra (Pisces, Galaxiidae) in northern Patagonian lakes

The family Galaxiidae exhibits a marked tendency toward morphological variation, particularly in characteristics related to feeding and caudal propulsion. The body shape of Aplochiton zebra from six Andean water bodies was examined and related to diet and to environmental characteristics such as transparency and predation risk. Although adults and larger juveniles showed no inter‐lake dependence in their morphology, smaller juveniles (SL < 40 mm) did show differences in eye diameter and dorsal fin length. Aplochiton zebra juveniles from Lake Puelo, where transparency showed the minimum value, have the largest eyes; those from Lake Futalaufquen with high transparency values have the smallest eyes. No clear relationship to predation risk was established. In Futalaufquen, Puelo and Rivadavia lakes the relationship between the principal components for morphology and for diet indicates, at least in part, that variation in body shape – and particularly traits related to swimming ability – could be related to diet.     

Records of the land planarian Polycladus gayi (Tricladida,Geoplanidae) preying on black snails Macrocyclis peruvianus (Gastropoda,Macrocyclidae)

Polycladus gayi is a colourful and easily recognizable land planarian native to the temperate to cold rainforests of the west coast of southern South America, in Chile and Argentina; however, its ecology is poorly understood. Here, we describe the first records of P. gayi preying on a black snail Macrocyclis peruvianus in the wild. Two events were recorded, the first in a healthy forest in Llancahue Alto, Panguipulli, Chile, during the austral summer of 2023, and the second in a mature evergreen forest in the coastal range of La Union, Chile. These records expand our knowledge of the feeding habits and behaviour of P. gayi and add M. peruvianus to its prey list.     

The Maipo River as a biogeographical barrier to Liolaemus monticola (Tropiduridae) in the mountain ranges of central Chile

univariate and multivariate statistiscal analyses of 39 meristic characters recorded for 12 sample of the lizard Liolaemus monticola were used to compare geographical variation in morphology with chromosomal races north and south of the Maipo River in central Chile. This extends a previous morphological study in the Andes Range and confirms that the Maipo River is a biogeographical barrier that also separates chromosomal races in the Coast Rnage. The phenetic variation among samples in sufficient to diffenetiate the chromosomal races, and also distinguishes population of the Coast Range from those of the Andes within chromosomal races. A possible historical sequence of events that accounts for the pattern of morphological differentiation is advanced.     

Revision ofDoniophyton (Compositae, Barnadesioideae)

This revision describes, illustrates and documents morphological variation inDoniophyton (Compositae, Barnadesioideae), restricted to Argentina and Chile. Two species are recognized,D. anomalum andD. weddellii (sp. nova), possessing distinct morphological and chromosomal features, elevational tolerances, and nearly allopatric distributions.Doniophyton weddellii occurs primarily in central to northern Andean Chile and Argentina from 1900–4000 m a. s. l.;D. anomalum is found principally in centralwestern Argentina and south into Patagonia at 0–1800 m a. s. l. Close relationship exists withChuquiraga of subfam.Barnadesioideae. It is hypothesized thatDoniophyton evolved out ofChuquiraga in the high central Andes between Chile and Argentina. It is suggested thatD. weddellii differentiated first, correlating with an aneuploid chromosomal decrease from n = 27 (inChuquiraga) to n = 25. Further evolution and chromosomal decrease to n = 24 resulted inD. anomalum, with accompanying migration into southern Andes and Patagonia. Nomenclatural changes result from examination of protologues and type specimens:Doniophyton anomalum replaces the commonly used nameD. patagonicum, and a new species,D. weddellii, is described for the taxon masquerading under the routinely used superfluous nameD. andicola. This paper is dedicated with admiration and respect to emer. Univ.-Prof. DrFriedrich Ehrendorfer, one of the world's outstanding plant systematists, and a leading scientist and administrator of the Institute of Botany of the University of Vienna     

Morphological and Genetic Divergences in a Coral Reef Damselfish, Pomacentrus coelestis

Population differentiation is one of the main topics in evolutionary biology. Except the exploration of color variation, few studies focused on morphological divergences among populations of coral reef fishes. In this work, we studied morphological and genetic differentiation among populations of the damselfish, Pomacentrus coelestis, in the northwestern Pacific Ocean. The shapes of the mandible and the premaxilla were explored using geometric morphometric methods and the genetic structure was investigated using microsattelites. Various tests revealed significant shape variation among most P. coelestis populations for both skeletal units. Morphological variation of the mandible accompanies a genetic break between populations of mainland Japan and Okinawa-Taiwan. However, Mantel and Procrustes tests revealed no congruence between morphological and genetic structures. We illustrate that phenotypic plasticity and adaptive divergence are potential evolutionary mechanisms underlying shape difference among P. coelestis populations. An ecomorphological approach suggests that various diet could be related to shape variation of oral jaws.     

Biological control potentials of insect-parasitic nematode Rhabditis blumi (Nematoda: Rhabditida) for major cruciferous vegetable insect pests

Pathogenicity of Rhabditis blumi Sudhaus against major cruciferous insect pests was evaluated in the lab and greenhouse. In Petri-dish tests against the insects, including Artogeia rapae L., Mamestra brassicae L., and Plutella xylostella L., insect mortality by R. blumi and its associated bacteria was dose and time dependent, which increased with dose (0?C80 dauer juveniles/larva) and time increments. Pathogenicity against fourth-instar larvae was higher than the rate of corresponding third-instar larvae. The highest insect mortality rate was observed in fourth-instar larvae of P. xylostella, followed by A. rapae, and M. brassicae, with mortality rates of 93.5, 88.2, and 77.8?%, respectively. Lethal dose values at 50?% (LD₅₀) of R. blumi were 25.7 dauer juveniles/larva on P. xylostella; 28.0 dauer juveniles/larva on A. rapae; and 40.6 dauer juveniles/larva on M. brassicae, respectively. In greenhouse tests, P. xylostella larvae were most susceptible to nematodes, with insect reduction rate of 88.0?%. The rate varied with vegetable species and persistence time of live nematodes on vegetable leaves after spraying. Nematodes established in cadavers showed positive correlation with nematode dose, whereas nematode persistence on the leaf was inversely related to hours after treatment.     

A new species of Alopoglossus lizard (Squamata,Gymnophthalmidae) from the tropical Andes,with a molecular phylogeny of the genus

We describe a new species of Alopoglossus from the Pacific slopes of the Andes in northern Ecuador based on morphological and molecular evidence. The new species differs most significantly from all other congeners in having a double longitudinal row of widened gular scales, lanceolate dorsal scales in transverse rows, 29–32 dorsal scales in a transverse row at midbody, and 4 longitudinal rows of ventrals at midbody. It is most similar in morphology to A. festae, the only species of Alopoglossus currently recognized in western Ecuador. We analyze the phylogenetic relationships among species of Alopoglossus based on the mitochondrial gene ND4. Cis-Andean [east of the Andes] and Trans-Andean [west of the Andes] species are nested in two separate clades, suggesting that the uplift of these mountains had an important effect in the diversification of Alopoglossus. In addition, we present an updated key to the species of Alopoglossus.     

MICROEVOLUTION AND PHENOTYPIC PLASTICITY IN DONAX SERRA RODING (BIVALVIA: DONACIDAE) ON HIGH ENERGY SANDY BEACHES

Morphological differences between populations of the wedge clamDonax serra inhabiting two different coasts and biogeographicregions of South Africa were investigated. Both adults and juvenilesoccupied different positions along the beach gradient dependingon the coast: on the southeast coast adults occurred in themid intertidal and juveniles and recruits were low intertidalto subtidal; on the west coast the zonation pattern was reversed.Not only adults but also juvenile clams had shapes differingsignificantly between the two coasts; west coast clams werethinner, rounder and had a higher body density than the southeastones-recruits were less dense in the former coast. Differencesin shell shape between coasts are probably the result of directionalselection on the adults with the microevolutionary changes beingmaintained by geographical isolation. Shell density, on theother hand, seems to be environmentally determined through physiologicalcontrol of shell calcification, i.e. more mobile intertidalclams having lower shell density than less mobile subtidal clams.Ontogenetic changes in shape and density are presumably adaptiveand appear to be related to mobility, i.e. the larger, heavierand denser adults being more stable in the substrate, and thesmaller, thinner and less dense juveniles being more mobileand dispersive. Phenotypic plasticity in present D. serra populationsis an important factor that enabled this species to occupy differenthabitats and biogeographic regions and to survive 5 millionyears of environmental changes. ¹ Present address: Laboratory for Ecology and Aquaculture, ZoologicalInstitute, Katholic Universiteit, Leuven, Naamsestraat 59 B-3000,Leuven, Belgium. E-mail: agsoares{at}eudoramail.com (Received 15 October 1997; accepted 5 January 1998)     

Shaped by the past,acting in the present: transgenerational plasticity of anti‐predatory traits

Phenotypic expression can be altered by direct perception of environmental cues (within‐generation phenotypic plasticity) and by the environmental cues experienced by previous generations (transgenerational plasticity). Few studies, however, have investigated how the characteristics of phenotypic traits affect their propensity to exhibit plasticity within and across generations. We tested whether plasticity differed within and across generations between morphological and behavioral anti‐predator traits of Physa acuta, a freshwater snail. We reared 18 maternal lineages of P. acuta snails over two generations using a full factorial design of exposure to predator or control cues and quantified adult F₂ shell size, shape, crush resistance, and anti‐predator behavior – all traits which potentially affect their ability to avoid or survive predation attempts. We found that most morphological traits exhibited transgenerational plasticity, with parental exposure to predator cues resulting in larger and more crush‐resistant offspring, but shell shape demonstrated within‐generation plasticity. In contrast, we found that anti‐predator behavior expressed only within‐generation plasticity such that offspring reared in predator cues responded less to the threat of predation than control offspring. We discuss the consequences of this variation in plasticity for trait evolution and ecological dynamics. Overall, our study suggests that further empirical and theoretical investigation is needed in what types of traits are more likely to be affected by within‐generational and transgenerational plasticity.     

Cranial morphological variation of Dromiciops gliroides (Microbiotheria) along its geographical distribution in south-central Chile: A three-dimensional analysis

We analyzed the variation in cranial morphology of the marsupial Dromiciops gliroides along its distribution in south-central Chile. We evaluated whether the cranial morphological variation is congruent with the phylogeographic structure previously observed in this species. We built three-dimensional models of 69 crania on which we digitized 30 landmarks. We used standard geometric morphometric methods to extract and analyze the shape and size components of the crania. Our data showed a subtle but consistent cranial size and shape variation along the studied distributional range, suggesting a geographic variation pattern rather than a phylogeographic structuring. Indeed, our multivariate analyses recovered a subtle morphological differentiation between island and mainland populations, contrary to what is suggested by a former phylogeographic study. We detected that either the cranial size variation, as well as the insularity and the latitude could be important factors underlying the cranial shape changes. We suggest that an interplay of historical and contemporary processes could be shaping the morphological pattern observed in this marsupial.     

Morphological plasticity in response to shading in three Convolvulus species of different ecological breadth

We evaluated in common-garden experiments the morphological plasticity to shading of three Convolvulus species that occur in Chile and differ in ecological breadth. Convolvulus arvensis L. is a world weed distributed along the country, and is found in open as well as in shaded habitats. Convolvulus chilensis Pers. is a Chilean endemic species typical of coastal habitats, and is found in open to partially open sites. C. demissus choisy occurs only on slopes of the Andes of Chile and Argentina, habitats with high incidence of solar radiation. We hypothesized that the magnitude of phenotypic plasticity to shading of these species would correlate with their ecological breadth. Shading had a significant effect on internode length, petiole length, stem diameter, stem length, number of branches, leaf area, leaf shape, leaf biomass, and specific leaf area. Species differed in all the morphological traits except leaf biomass. A significant Shading × Species interaction in the two-way ANOVA, i.e. differential plasticity to shading of Convolvulus species, was found for petiole length, stem length, number of branches, leaf shape, and specific leaf area. Contrary to our hypothesis, tests of parallelism showed that, in general, the plasticity to shading of C. chilensis (the species of intermediate ecological breadth) was the greatest, and that of C. arvensis (the weed) and C. demissus (the species of narrow distribution) was similar. Issues of ecotype differentiation, in the case of C. arvensis, and the role of life history traits are raised to explain the observed lack of association between ecological breadth and magnitude of phenotypic plasticity.     

Phenotypic plasticity inPotamogeton (Potamogetonaceae)

Sources of the extensive morphological variation of the species and hybrids ofPotamogeton were studied, especially from the viewpoint of the stability of the morphological characters used inPotamogeton taxonomy. Transplant experiments, the cultivation of clones under different values of environmental factors, and the cultivation of different clones under uniform conditions were performed to assess the proportion of phenotypic plasticity in the total morphological variation. Samples from 184 populations of 41Potamogeton taxa were grown. The immense range of phenotypic plasticity, which is possible for a single clone, is documented in detail in 14 well-described examples. The differences among distinct populations of a single species observed in the field were mostly not maintained when grown together under the same environmental conditions. Clonal material cultivated under different values of environmental factors produced distinct phenotypes, and in a few cases a single genotype was able to demonstrate almost the entire range of morphological variation in an observed trait known for that species. Several characters by recent literature claimed to be suitable for distinguishing varieties or even species were proven to be dependent on environmental conditions and to be highly unreliable markers for the delimiation of taxa. The unsatisfactory taxonomy that results when such classification of phenotypes is adopted is illustrated by three examples from recent literature. Phenotypic plasticity was found to be the main source of morphological variation within the species ofPotamogeton, having much more influence than morphological differences caused by different genotypes.     

Ciliary Rootlet Coiled-Coil 2 (crocc2) Is Associated with Evolutionary Divergence and Plasticity of Cichlid Jaw Shape

Cichlid fishes exhibit rapid, extensive, and replicative adaptive radiation in feeding morphology. Plasticity of the cichlid jaw has also been well documented, and this combination of iterative evolution and developmental plasticity has led to the proposition that the cichlid feeding apparatus represents a morphological “flexible stem.” Under this scenario, the fixation of environmentally sensitive genetic variation drives evolutionary divergence along a phenotypic axis established by the initial plastic response. Thus, if plasticity is predictable then so too should be the evolutionary response. We set out to explore these ideas at the molecular level by identifying genes that underlie both the evolution and plasticity of the cichlid jaw. As a first step, we fine-mapped an environment-specific quantitative trait loci for lower jaw shape in cichlids, and identified a nonsynonymous mutation in the ciliary rootlet coiled-coil 2 (crocc2), which encodes a major structural component of the primary cilium. Given that primary cilia play key roles in skeletal mechanosensing, we reasoned that this gene may confer its effects by regulating the sensitivity of bone to respond to mechanical input. Using both cichlids and zebrafish, we confirmed this prediction through a series of experiments targeting multiple levels of biological organization. Taken together, our results implicate crocc2 as a novel mediator of bone formation, plasticity, and evolution.     

Trophic plasticity and foraging performance in red drum, Sciaenops ocellatus (Linnaeus)

Matching behavior, morphology, or physiology to current environments based on experience or cues can be an adaptive solution to environmental change. We examined morphological and behavioral plasticity induced by durophagy (consumption of hard foods) in red drum (Sciaenops ocellatus), an ecologically and recreationally important fish species undergoing stock enhancement. At the conclusion of the experiment, we conducted feeding performance trials to address the potential adaptive significance of diet-induced traits. Relative to soft foods, hard food induced a deeper head in the area of the pharyngeal mill, anterio-dorsally shifted eyes, and 8% heavier feeding muscles in juvenile S. ocellatus. These fish initially consumed hard food 2.6 times faster than fish raised on soft food. However, in subsequent feeding trials, handling time rapidly converged until both groups appeared equally efficient. This result indicates that learning may compensate for small magnitude morphological differences within a species. We discuss the importance of performance trials for testing the adaptive significance of induced plasticity and the value of separating behavioral and morphological development in studies of phenotypic plasticity. We conclude with a discussion on the implications of our results for successful supplementation of wild populations.     

Location,location, location: larvae position inside the nest is correlated with adult body size in worker bumble-bees (Bombus impatiens)

Social insects display task-related division of labour. In some species, division of labour is related to differences in body size, and worker caste members display morphological adaptations suited for particular tasks. Bumble-bee workers (Bombus spp.) can vary in mass by eight- to tenfold within a single colony, which previous work has linked to division of labour. However, little is known about the proximate mechanism behind the production of this wide range of size variation within the worker caste. Here, we quantify the larval feeding in Bombus impatiens in different nest zones of increasing distance from the centre. There was a significant difference in the number of feedings per larva across zones, with a significant decrease in feeding rates as one moved outwards from the centre of the nest. Likewise, the diameter of the pupae in the peripheral zones was significantly smaller than that of pupae in the centre. Therefore, we conclude that the differential feeding of larvae within a nest, which leads to the size variation within the worker caste, is based on the location of brood clumps. Our work is consistent with the hypothesis that some larvae are ‘forgotten’, providing a possible first mechanism for the creation of size polymorphism in B. impatiens.     

Age and growth of the Antarctic dragonfish Parachaenichthys charcoti (Pisces, Bathydraconidae) from the southern Scotia Arc

The Antarctic dragonfish Parachaenichthys charcoti is commonly found in shelf waters of islands in the southern Scotia Arc. Its northern congener P. georgianus is distributed on the shelves of South Georgia and the South Sandwich Islands. Biological information on P. charcoti is limited and restricted largely to reproductive traits and feeding habits. The present study fills this gap, providing the first data on age and growth of this species by otolith reading. Age was estimated in juveniles and adults by counting annuli on otoliths. Age of early juveniles was determined by microincrement counts (considered to be daily rings). Age estimates of juveniles and adults ranged from 1 to 9?years, with a high percentage agreement between readings and low values of counting variability indices APE (3.3?%) and CV (4.7?%). Age of early juveniles ranged from 160 to 204?days, all showing an evident check at 32–35?days of age, tentatively linked to the first larval exogenous feeding. The estimated values of von Bertalanffy growth parameters L _∞ and k were 53.55?cm and 0.22, respectively, and the index of growth performance P was 2.33. Hatching in P. charcoti takes place in late winter, from August to September. Compared to other notothenioids inhabiting the Seasonal Pack-ice Zone, P. charcoti is a relatively fast growing species with moderate longevity, sharing several biological characteristics with its sister species P. georgianus.     

Morphometric Variation on the Cypress Aphid Cinara cupressi (Buckton) (Hemiptera: Aphididae) Associated to Urban Trees

Cinara cupressi (Buckton) is an important aphid pest of the Cupressaceae family, originally reported in Chile in 2003. Since then, it has spread over 4,000 km, contributing to conservation issues, mostly associated with native and urban trees of the Cupressaceae. In the present work, the morphometric variation of C. cupressi was examined to determine if the species present in Chile corresponds to a specific entity, and to identify variations among specimens from different localities in the study area. Colonies were collected from urban trees from northern, central, and southern Chile. Morphometric data for 14 characters in aphids from 63 localities in all the distribution ranges were measured and analyzed by multivariate analysis. Results showed that the species present in Chile corresponds to C. cupressi like a single specific entity, showing no morphological variation across the regions sampled. Our data will be discussed within the context of correct taxonomic identification for the implementation of effective biological control strategies.