Connectivity in the cold: the comparative population genetics of vent‐endemic fauna in the Scotia Sea,Southern Ocean

We report the first comparative population genetics study for vent fauna in the Southern Ocean using cytochrome C oxidase I and microsatellite markers. Three species are examined: the kiwaid squat lobster, Kiwa tyleri, the peltospirid gastropod, Gigantopelta chessoia, and a lepetodrilid limpet, Lepetodrilus sp., collected from vent fields 440 km apart on the East Scotia Ridge (ESR) and from the Kemp Caldera on the South Sandwich Island Arc, ~95 km eastwards. We report no differentiation for all species across the ESR, consistent with panmixia or recent range expansions. A lack of differentiation is notable for Kiwa tyleri, which exhibits extremely abbreviated lecithotrophic larval development, suggestive of a very limited dispersal range. Larval lifespans may, however, be extended by low temperature‐induced metabolic rate reduction in the Southern Ocean, muting the impact of dispersal strategy on patterns of population structure. COI diversity patterns suggest all species experienced demographic bottlenecks or selective sweeps in the past million years and possibly at different times. ESR and Kemp limpets are divergent, although with evidence of very recent ESR‐Kemp immigration. Their divergence, possibility indicative of incipient speciation, along with the absence of the other two species at Kemp, may be the consequence of differing dispersal capabilities across a ~1000 m depth range and/or different selective regimes between the two areas. Estimates of historic and recent limpet gene flow between the ESR and Kemp are consistent with predominantly easterly currents and potentially therefore, cross‐axis currents on the ESR, with biogeographic implications for the region.     

Effect of the endosymbiotic pea crab Calyptraeotheres garthi on the metabolic rate and oxidative status of the slipper limpet Crepidula cachimilla

Parasites may induce metabolic changes and imbalances in the redox status of hosts. This study tested the effect of parasites on the O₂ consumption rate (O₂‐CR) of hosts, and explored the link between O₂‐CR and oxidative stress in parasitized hosts. We used the symbiotic pea crab Calyptraeotheres garthi and its slipper limpet host Crepidula cachimilla as models. The O₂‐CR of long‐term (3 months) infested limpets was 2.5 times greater than that of long‐term uninfested limpets. Also, the O₂‐CR of limpets stripped of crabs 24 h before measurements was intermediate between that of long‐term infested and uninfested limpets. These results indicate a parasitic relationship between C. garthi and Cr. cachimilla, and suggest that the effect of the parasite on the metabolic rate of limpets is reversible. Lastly, the activity of two antioxidant enzymes (CAT and GST) as well as lipid peroxidation did not vary between infested and uninfested limpets. Thus, increased O₂‐CR is not necessarily coupled with oxidative stress in pea crab‐parasitized slipper limpets.     

Another step towards understanding the slit‐limpets (Fissurellidae,Fissurelloidea, Vetigastropoda,Gastropoda): a combined five‐gene molecular phylogeny

Aktipis, S. W., Boehm, E. & Giribet, G. (2010). Another step towards understanding the slit‐limpets (Fissurellidae, Fissurelloidea, Vetigastropoda, Gastropoda): a combined five‐gene molecular phylogeny. —Zoologica Scripta, 40, 238–259. Fissurellids, commonly known as slit or keyhole limpets, are limpet‐shaped gastropods that typically possess a hole, slit or notch in their bilaterally symmetrical shells and usually occur on rocky marine substrates. Competing classifications for Fissurellidae have been circumscribed using various morphological characters such as radular, shell and mantle features; two to five different subfamilies have been recognized. Although fissurellid species are frequently included in larger vetigastropod phylogenies, relatively few phylogenetic studies of the group have been performed. This study presents a phylogenetic investigation of the relationships amongst slit‐limpets in the vetigastropod superfamily Fissurelloidea, representing the first molecular phylogeny of this clade. In this study, the monophyly of Fissurelloidea and Fissurellidae varied depending on the analytical method used, but clades compatible with the subfamilies Diodorinae and Fissurellinae were recovered with high bootstrap support in all analyses. Species traditionally classified in Emarginulinae formed two groups identified in this study as Hemitominae (Puncturella, Cranopsis and Hemitoma) and Emarginulinae sensu stricto (Emarginula, Montfortula, Tugali, Scutus and Nannoscutum), but Hemitominae was only monophyletic in the maximum likelihood analysis. The results of this study contradict traditional fissurellid classifications as well as theories about the evolution of key fissurellid shell characters. The placement of Puncturella, Cranopsis and Hemitoma sister to all remaining fissurellids suggests that the presence of an anteriorly placed foramen or notch is plesiomorphic, and that an anterior notch or slit evolved multiple times in Fissurellidae.     

Oysters as habitat for limpets in a temperate mangrove forest

In temperate mangrove forests in New South Wales, Australia, the limpet Patelloida mimula Iredale lives on the oyster Saccostrea commercialis Iredale and Roughley, which, along with mangrove trees, provide the only hard substrata in a habitat otherwise dominated by soft-sediment. The objective of this study was to ascertain the degree of association between the limpet and the oyster by examining their patterns of co-occurrence in the forest and the relationship between individual pairs of limpets and oysters. Sampling of the distribution and abundance of limpets and oysters throughout the mangrove forest revealed that limpets were rarely present on substrata other than oysters. Patterns of abundance of limpets were, however, not directly related to the amount of habitat provided by the oysters. For example, there was a dramatic decline in the abundance of oysters from seaward to landward in the mangrove forest which was not reflected in the densities of limpets. Consequently, oysters appear to set the limits of distribution of limpets, but other factors modify their broad-scale patterns of distribution and abundance within these bounds. Limpets leave scars on oysters which might be home sites. About 98% of oysters with limpets had only one limpet per surface of oyster, and the distribution of limpets was overdispersed or repulsed. Moreover, in some areas of the forest, the lengths of limpets were directly related to lengths of oysters. Tracking of individual limpets for 13 days revealed that > 70% remained on the same scar of an oyster. This evidence suggests that for some limpets there is a strong association with particular oysters. Factors determining the distribution, abundance, and sizes of oysters are likely to be important sources of variation to the structure of populations of P. mimula in temperate mangrove forests.     

The knock‐down of the expression of MdMLO19 reduces susceptibility to powdery mildew (Podosphaera leucotricha) in apple (Malus domestica)

Varieties resistant to powdery mildew (PM; caused by Podosphaera leucotricha) are a major component of sustainable apple production. Resistance can be achieved by knocking‐out susceptibility S‐genes to be singled out among members of the MLO (Mildew Locus O) gene family. Candidates are MLO S‐genes of phylogenetic clade V up‐regulated upon PM inoculation, such as MdMLO11 and 19 (clade V) and MdMLO18 (clade VII). We report the knock‐down through RNA interference of MdMLO11 and 19, as well as the complementation of resistance with MdMLO18 in the Arabidopsis thaliana triple mlo mutant Atmlo2/6/12. The knock‐down of MdMLO19 reduced PM disease severity by 75%, whereas the knock‐down of MdMLO11, alone or in combination with MdMLO19, did not result in any reduction or additional reduction of susceptibility compared with MdMLO19 alone. The test in A. thaliana excluded a role for MdMLO18 in PM susceptibility. Cell wall appositions (papillae) were present in both PM‐resistant and PM‐susceptible plants, but were larger in resistant lines. No obvious negative phenotype was observed in plants with mlo genes knocked down. Apparently, MdMLO19 plays the pivotal role in apple PM susceptibility and its knock‐down induces a very significant level of resistance.     

Trophic relationships between the kelp gull and the Antarctic limpet at King George Island (South Shetland Islands, Antarctica) during the breeding season

The diet of the kelp gull (Larus dominicanus), its foraging behaviour and the consumption rates on the Antarctic limpet (Nacella concinna) were studied during austral spring and summer 1992/1993 and 1993/1994 at Potter Peninsula, King George Island, Antarctica. Prey information was obtained by collecting 237 pellets, foraging behaviour was observed by focal and instantaneous scan samplings, and consumption rate was estimated by means of weekly sampling of limpets found in 5 nests and their respective middens. Limpets were the most important prey followed by scavenged prey (penguin and seal carcasses), amphipods, snails, fish and euphausiids. Foraging gulls spent 51% of the time searching for limpets, 10% moving between foraging areas, 9% in catching effort and 15% handling prey. The number of gulls observed searching for limpets was inversely correlated with the tidal height. In the diet limpets provide 102.3, 159.4 and 188.1 kJ gull⁻¹ day⁻¹ during incubation, hatching and brooding respectively; these values range between 15 and 27%, with a maximum of 40%, of the basic daily energy requirements of kelp gulls. Total consumption rate estimations for the whole population of gulls at Potter Peninsula reached between 3400 and 4800 limpets day⁻¹, which represents approximately 10–14% of the total annual limpet mortality. Received: 25 March 1996 / Accepted: 26 August 1996     

An analysis of distribution and abundance of populations of the high-shore limpet,Notoacmea petterdi (tenison-woods)

Summary Notoacmea petterdi occurs only on vertical surfaces at the highest levels on the shore. On a given surface, density of limpets decreases with increasing height. Mean and maximum sizes of limpets increase with increasing height, due to faster rates of growth at higher levels where densities are lower. Rates of mortality are also negatively correlated with height on the shore, and are therefore generally less at higher levels. Both adult and juvenile limpets exhibit well-developed homing behaviour. There is no evidence of seasonal migrations, density-dependent migrations, nor gradual upward migrations as limpets grow older.Hypotheses are formed on the basis of these preliminary observations and measurements. Results of subsequent experimental manipulations of densities support the hypothesis that density-dependent mortality, due to intraspecific competition, plays a major role in regulating population densities of this limpet. It is also suggested that the pattern of settlement of juvenile limpets is the major factor that determines the limits to the vertical distribution of this species.     

Molecular signatures of host specificity linked to habitat specialization in Exaiptasia sea anemones

Rising ocean temperatures associated with global climate change induce breakdown of the symbiosis between coelenterates and photosynthetic microalgae of the genus Symbiodinium. Association with more thermotolerant partners could contribute to resilience, but the genetic mechanisms controlling specificity of hosts for particular Symbiodinium types are poorly known. Here, we characterize wild populations of a sea anemone laboratory model system for anthozoan symbiosis, from contrasting environments in Caribbean Panama. Patterns of anemone abundance and symbiont diversity were consistent with specialization of holobionts for particular habitats, with Exaiptasia pallida/S. minutum (ITS2 type B1) abundant on vertical substrate in thermally stable, shaded environments but E. brasiliensis/Symbiodinium sp. (ITS2 clade A) more common in shallow areas subject to high temperature and irradiance. Population genomic sequencing revealed a novel E. pallida population from the Bocas del Toro Archipelago that only harbors S. minutum. Loci most strongly associated with divergence of the Bocas‐specific population were enriched in genes with putative roles in cnidarian symbiosis, including activators of the complement pathway of the innate immune system, thrombospondin‐type‐1 repeat domain proteins, and coordinators of endocytic recycling. Our findings underscore the importance of unmasking cryptic diversity in natural populations and the role of long‐term evolutionary history in mediating interactions with Symbiodinium.     

Defensive responses to predatory seastars by two specialist limpets, Notoacmea insessa (Hinds) and Collisella instabilis (Gould), associated with marine algae

The limpets Notoacmea insessa (Hinds) and Collisella instabilis (Gould), which are associated specifically with certain algae, were tested for defensive responses to seastars. Contact with predatory seastars elicited responses by both species of limpets, in contrast to previous work reporting a lack of defensive responses by specialist limpets associated with plants. Non-predatory seastars normally did not elicit defensive responses. The form of the response by Notoacmea insessa differed, depending on whether the limpet was on or off its grazing scar. When the limpet was off its grazing scar, the most common response was movement away from the point of contact. When on the scar, the limpet usually elevated its shell and rocked from side-to-side, but rarely moved from the scar. The responses of Collisella instabilis almost always involved rapid movement away from the point of contact and tended to be more vigorous than those of Notoacmea insessa.     

Classification of crucigenoid algae: phylogenetic position of the reinstated genus Lemmermannia,Tetrastrum spp. Crucigenia tetrapedia,and C. lauterbornii (Trebouxiophyceae,Chlorophyta)1

The subfamily Crucigenioideae was traditionally classified within the well‐characterized family Scenedesmaceae (Chlorophyceae). Several morpho‐logical revisions and questionable taxonomic changes hampered the correct classification of crucigenoid species resulting in a high number of synonymous genera. We used a molecular approach to determine the phylogenetic position of several Tetrastrum and Crucigenia species. The molecular results were correlated with morphological and ontogenetic characters. Phylogenetic analyses of the SSU rDNA gene resolved the position of Tetrastrum heteracanthum and T. staurogeniaeforme as a new lineage within the Oocystis clade of the Trebouxiophyceae. Crucigenia tetrapedia, T. triangulare, T. punctatum, and T. komarekii were shown to be closely related to Botryococcus (Trebouxiophyceae) and were transferred to Lemmer‐mannia. Crucigenia lauterbornii was not closely related to the other Crucigenia strains, but was recovered within the Chlorella clade of the Trebouxiophyceae.     

Population genetic data of a model symbiotic cnidarian system reveal remarkable symbiotic specificity and vectored introductions across ocean basins

The Aiptasia–Symbiodinium symbiosis is a promising model for experimental studies of cnidarian–dinoflagellate associations, yet relatively little is known regarding the genetic diversity of either symbiotic partner. To address this, we collected Aiptasia from 16 localities throughout the world and examined the genetic diversity of both anemones and their endosymbionts. Based on newly developed SCAR markers, Aiptasia consisted of two genetically distinct populations: one Aiptasia lineage from Florida and a second network of Aiptasia genotypes found at other localities. These populations did not conform to the distributions of described Aiptasia species, suggesting that taxonomic re‐evaluation is needed in the light of molecular genetics. Associations with Symbiodinium further demonstrated the distinctions among Aiptasia populations. According to 18S RFLP, ITS2‐DGGE and microsatellite flanker region sequencing, Florida anemones engaged in diverse symbioses predominantly with members of Symbiodinium Clades A and B, but also C, whereas anemones from elsewhere harboured only S. minutum within Clade B. Symbiodinium minutum apparently does not form a stable symbiosis with other hosts, which implies a highly specific symbiosis. Fine‐scale differences among S. minutum populations were quantified using six microsatellite loci. Populations of S. minutum had low genotypic diversity and high clonality (R = 0.14). Furthermore, minimal population structure was observed among regions and ocean basins, due to allele and genotype sharing. The lack of genetic structure and low genotypic diversity suggest recent vectoring of Aiptasia and S. minutum across localities. This first ever molecular‐genetic study of a globally distributed cnidarian and its Symbiodinium assemblages reveals host–symbiont specificity and widely distributed populations in an important model system.     

Molecular and morphological criteria for revision of the genus Microcoleus (Oscillatoriales,Cyanobacteria)

Ninety‐two strains of Microcoleus vaginatus (=nomenclatural‐type species of the genus Microcoleus Desmazières ex Gomont) and Phormidium autumnale Trevisan ex Gomont from a wide diversity of regions and biotopes were examined using a combination of morphological and molecular methods. Phylogenies based on the 16S rDNA and 16S‐23S ITS (partial) demonstrated that the 92 strains, together with a number of strains in GenBank, were members of a highly supported monophyletic clade of strains (Bayesian posterior probability = 1.0) distant from the species‐cluster containing the generitype of Phormidium. Similarity of the 16S rRNA gene exceeded 95.5% among all members of the Microcoleus clade, but was less than 95% between any Microcoleus strains and species outside of the clade (e.g., Phormidium sensu stricto). These findings, which are in agreement with earlier studies on these taxa, necessitate the revision of Microcoleus to include P. autumnale. Furthermore, the cluster of Phormidium species in the P. autumnale group (known as Group VII) must be moved into Microcoleus as well, and these nomenclatural transfers are included in this study. The main diacritical characters defining Microcoleus are related to the cytomorphology of trichomes, including: narrowed trichome ends, calyptra, cells shorter than wide up to more or less isodiametric, and facultative presence of sheaths. The majority of species are 4–10 μm in diameter. The possession of multiple trichomes in a common sheath is present facultatively in many but not all species.     

Mutualism between the territorial intertidal limpet Patella longicosta and the crustose alga Ralfsia verrucosa

Mutualistic relations between plants and animals are well documented on land but have received less attention in marine systems. This study examined the relationship between the territorial intertidal limpet Patella longicosta and the crustose brown alga Ralfsia verrucosa. Adult Patella are found exclusively in association with Ralfsia, on which they feed, while Ralfsia occurs primarily, but not exclusively, in Patella territories. Ralfsia benefits directly from both the presence and the territorial behaviour of Patella. Algal productivity was assessed by measuring oxygen evolution and utilization in situ and deriving photosynthesis/irradiance curves. Productivity was increased by about 30% by the presence of Patella in both summer (P _max of grazed algae 0.0098; ungrazed algae 0.0063 mg C · cm^-2 · h^-1) and winter (P _max grazed algae 0.0081; ungrazed algae 0.0053 mg^-2 · C · h^-1). Algal growth rates were not significantly increased by the application of limpet mucus in the laboratory. We did not examine nutrient regeneration by the limpet, but the increase in photosynthetic rate may depend on the limpet's grazing pattern which creates secondary sites for growth. Ralfsia also benefited from the territorial behaviour of Patella. The effects of different grazing regimes were investigated in different seasons by removing territorial limpets and either excluding all limpets using copper-based antifouling paint, or allowing access to non-territorial limpets (mostly P. oculus) using partial paint barriers. Exclusion of all limpets resulted in rapid overgrowth of Ralfsia plants by the foliose green alga Ulva sp.. Where non-territorial limpets had access to the plants overgrowth was reduced but Ralfsia plants were entirely removed by destructive grazing. Non-territorial grazers removed 90% of Ralfsia plants within 4 weeks in summer and 60% in winter. In control treatments P. longicosta prevented overgrowth by Ulva and actively excluded vagrant grazers, preventing overgrazing. Based on these findings, the association between the limpet and alga can be regarded as a nonobligate mutualism.     

Comparative analysis of Arabidopsis UGT74 glucosyltransferases reveals a special role of UGT74C1 in glucosinolate biosynthesis

The study of glucosinolates and their regulation has provided a powerful framework for the exploration of fundamental questions about the function, evolution, and ecological significance of plant natural products, but uncertainties about their metabolism remain. Previous work has identified one thiohydroximate S‐glucosyltransferase, UGT74B1, with an important role in the core pathway, but also made clear that this enzyme functions redundantly and cannot be the sole UDP‐glucose dependent glucosyltransferase (UGT) in glucosinolate synthesis. Here, we present the results of a nearly comprehensive in vitro activity screen of recombinant Arabidopsis Family 1 UGTs, which implicate other members of the UGT74 clade as candidate glucosinolate biosynthetic enzymes. Systematic genetic analysis of this clade indicates that UGT74C1 plays a special role in the synthesis of aliphatic glucosinolates, a conclusion strongly supported by phylogenetic and gene expression analyses. Finally, the ability of UGT74C1 to complement phenotypes and chemotypes of the ugt74b1‐2 knockout mutant and to express thiohydroximate UGT activity in planta provides conclusive evidence for UGT74C1 being an accessory enzyme in glucosinolate biosynthesis with a potential function during plant adaptation to environmental challenge.     

HT proteins contribute to S‐RNase‐independent pollen rejection in Solanum

Plants have mechanisms to recognize and reject pollen from other species. Although widespread, these mechanisms are less well understood than the self‐incompatibility (SI) mechanisms plants use to reject pollen from close relatives. Previous studies have shown that some interspecific reproductive barriers (IRBs) are related to SI in the Solanaceae. For example, the pistil SI proteins S‐RNase and HT protein function in a pistil‐side IRB that causes rejection of pollen from self‐compatible (SC) red/orange‐fruited species in the tomato clade. However, S‐RNase‐independent IRBs also clearly contribute to rejecting pollen from these species. We investigated S‐RNase‐independent rejection of Solanum lycopersicum pollen by SC Solanum pennellii LA0716, SC. Solanum habrochaites LA0407, and SC Solanum arcanum LA2157, which lack functional S‐RNase expression. We found that all three accessions express HT proteins, which previously had been known to function only in conjunction with S‐RNase, and then used RNAi to test whether they also function in S‐RNase‐independent pollen rejection. Suppressing HT expression in SC S. pennellii LA0716 allows S. lycopersicum pollen tubes to penetrate farther into the pistil in HT suppressed plants, but not to reach the ovary. In contrast, suppressing HT expression in SC. Solanum habrochaites LA0407 and in SC S. arcanum LA2157 allows S. lycopersicum pollen tubes to penetrate to the ovary and produce hybrids that, otherwise, would be difficult to obtain. Thus, HT proteins are implicated in both S‐RNase‐dependent and S‐RNase‐independent pollen rejection. The results support the view that overall compatibility results from multiple pollen–pistil interactions with additive effects.     

MOLECULAR PHYLOGENY OF THE HETEROTROPHIC DINOFLAGELLATES,PROTOPERIDINIUM, DIPLOPSALIS AND PREPERIDINIUM (DINOPHYCEAE), INFERRED FROM LARGE SUBUNIT rDNA1

The genera Protoperidinium Bergh, Diplopsalis Bergh, and Preperidinium Mangin, comprised of species of marine, thecate, heterotrophic dinoflagellates in the family Protoperidinaceae Balech, have had a confused taxonomic history. To elucidate the validity of morphological groupings within the Protoperidinium and diplopsalids, and to determine the evolutionary relationships between these and other dinoflagellates, we undertook a study of molecular phylogeny using the D1–D3 domains of the large subunit (LSU) of the rDNA. Based on morphology, the 10 Protoperidinium species examined belonged to three subgenera and five morphological sections. Two diplopsalid species were also included. Single‐cell PCR, cloning, and sequencing revealed a high degree of intraindividual sequence variability in the LSU rDNA. The genus Protoperidinium appeared to be recently divergent in all phylogenetic analyses. In maximum parsimony and neighbor joining analyses, Protoperidinium formed a monophyletic group, evolving from diplopsalid dinoflagellates. In maximum likelihood and Bayesian analyses, however, Protoperidinium was polyphyletic, as the lenticular, diplopsalid heterotroph, Diplopsalis lenticula Bergh, was inserted within the Protoperidinium clade as basal to Protoperidinium excentricum (Paulsen) Balech, and Preperidinium meunieri (Pavillard) Elbrächter fell within a separate clade as a sister to the Oceanica and Protoperidinium steidingerae Balech. In all analyses, the Protoperidinium were divided into two major clades, with members in the Oceanica group and subgenus Testeria in one clade, and the Excentrica, Conica, Pellucida, Pyriforme and Divergens sections in the other clade. The LSU rDNA molecular phylogeny supported the historical morphologically determined sections, but not a simple morphology based model of evolution based on thecal plate shape.