Sciency Thoughts: Lycopsidae

Showing posts with label Lycopsidae. Show all posts

Wednesday, 15 November 2017

Ocyale ghost: A new species of Wolf Spider from Madagascar.

Wolf Spiders, Lycosidae, are large, active Spiders that do not build webs, ambushing animals that passes close to their burrows or actively seeking out and chasing down prey. They have large prominent eyes, and a habit of carrying their eggs in a sack on their abdomens. Members of the genus Ocyale are found in Africa, Asia and the America's though it is thought likely that all American and possibly Asian species may have been placed in this genus erroneously.

In a paper published in the European Journal of Taxonomy on 3 October 2017, Merlijn Jocque of the Biodiversity Inventory for Conservation, Operation Wallacea, and Aquatic and Terrestrial Ecology at the Royal Belgian Institute of Natural Sciences, Siel Wellens, also of Biodiversity Inventory for Conservation and Operation Wallacea, J Andianarivosoa and Felix Rakotondraparany of Mention Zoologie et Biologie Animale at the Université d’Antananarivo, Sam The Seing of Development and Biodiversity Conservation Action for Madagascar, and Rudy Jocqué of the Royal Museum for Central Africa, describe a new species of Ocyale from Mahajanga Province in Madagascar.

The new species is named Ocyale ghost, in reference to its white colour and in addition the white Wolf 'Ghost in the book Game of Thrones by George R.R. Martin. It is a moderately large Spider, with males reaching 16.76–19.45 mm and females 16.47–22.01 mm, creamy white in colour with darker spots and yellow rings around the eyes. The species was found only on the white sandy beaches surrounding Lake Matsedroy.

Ocyale ghost, female photographed at type locality. Jocque et al. (2017).

Thursday, 4 February 2016

Lycopsid Trees from the earliest Late Devonian of Svalbad Island, Norway.

The evolution of Trees is considered to be a key development in the colonization of land by life, creating a range of new habittats as well as raising oxygen levels and stabilizing soils for the first time. The earliest known fossil forest comes from the late Middle Devonian of Gilboa in New York State, and comprises a diverse assemblage of trees including Archaeopteridaleans (trees with woody trunks and leafy branches probably related to living Conifers), Pseudosporochnaleans (small to medium trees showing some morphological similarity to living Tree Ferns and Palms), and Lycopsids (Giant Club Mosses). Lycopsid Trees are known from a variety of other fossil forest sites, as well as individual floated Trees in marine sediments through the Late Devonian, and were a major part of the flora of the Carboniferous Coal forests.

In a paper published in the journal Geology on 24 November 2015, Christopher Berry of the School of Earth and Ocean Sciences at Cardiff University and John Marshall of the National Oceanography Centre at the University of Southampton discuss a fossil Lycopsid forest from the Plantekløfta Formation at Munindalen on Svalbard Island in the Norwegian Arctic.

The Plantekløfta Formation has previously been described as being Latest Devonian in age, but examination of palynological evidence (preserved pollen and spores) by Berry and Marshall leads them to conclude that the deposits in fact date from the earliest Late Devonian, making these deposits only a little younger than those at Gilboa.

The formation is exposed at three localities, each showing numerous Lycopsid stumps preserved in situ, many having extensive root systems as well as variable amounts of upright trunk, with the largest trunks being about 100 mm across. These have previously been described as Archaeosigillaria, but which Berry and Marshall consider to belong to the species Protolepidodendropsis pulchra, which has previously only been described from isolated specimens from marine deposits identified as floating logs.

In-situ Lycopsid fossils. (H) Locality AF3, partial trunk in situ, base sheared by small fault (arrow), showing variation of level of preservation in cortex from oval leaf base parenchyma at base to diamond-shaped leaf bases at top. (I) Locality AF1, upright trunk with slightly flared base. (J,K) Locality AF2 Sandstone cast base removed from loose shale, showing flaring of extreme basal portion and separation of diamond leaf bases by secondary expansion. Scale bars are 50 mm. Berry & Marshall (2015).

Although it is located within the Arctic Circle today, during the Devonian Svalbad was close to the equator, so that the forests of Plantekløfta would have been tropical in nature. The roots of the trees are preserved in a palaeosol (fossil soil), but the upper parts are preserved in a conglomerate; a sedimentary deposit comprising a mixture of rock types, typically associated with landslides, floods or similar catastrophic events. The upper layers of this contain amorphous organic matter, thought to have been formed in an anoxic lake. Berry and Marshall interpret this as being a rapidly subsiding lake basin with aluvial sediments being deposited by a river or river entering from the west and forming a fan or delta.

The trees apparently lived in monospecific stands (stands of a single species of tree), quite unlike the forests of Gilboa, which were diverse in nature with a diverse range of trees living alongside one another. Since the Gilboan forest is slightly older, this cannot imply that the Plantekløfta forest predates the evolution of a wider range of trees, suggesting that this a reflection of the forests ecology. This is contrary to modern expectations, with a diverse tree assemblage in Gilboa, thought to have had a dry temperate climate, but a low diversity forest in the wet tropics at Plantekløfta.

Saturday, 4 October 2014

How an invasive Grass species makes American Toads more vulnerable to Wolf Spiders.

Invasive plants can significantly modify local habitats, particularly if they lack herbivores in the environments they are colonising, by both modifying the structure of the environment and excluding native plants which provide food and homes to native animals. One such plant is the Japanese Stilt Grass (Microstegium vimineum), which has invaded moist forest-floor environments across the eastern United States. Japanese Stilt Grass has been shown to modify soil chemistry and Arthropod diversity and abundance in areas where it invades, and lacks any significant herbivores in the United States, allowing it to spread with little impediment.

Japanese Stilt Grass, Microstegium vimineum. Theresa Yednock/National Park Service/Wikimedia Commons.

One Vertebrate species is also apparently affected by the presence of Japanese Stilt Grass, the American Toad (Anaxyrus americanus), which appears to decline where the Grass becomes established. This could potentially be for a number of reasons. Firstly, like all Amphibians, American Toads have permeable skin through which they exchange fluids and gasses with the environment, which may make them vulnerable to changes in soil chemistry. Secondly they feed almost exclusively on Arthropod prey, notably Mites and Ticks (Acari), Spiders (Araneae), Beetles (Coleoptera), Springtails (Collembola), Flies (Diptera), Bugs (Hemiptera), and Ants, Bees and Wasps (Hymenoptera) and changes in the abundance of these prey items may affect the survival of the Toads. Finally the Toads themselves are vulnerable to predation by larger Arthropods, as they metamorphose (change from tadpoles into adult Toads) very young, achieving most of their growth in the terrestrial environment.

American Toad, Anaxyrus americanus. Brad Glorioso/National Wetlands Research Center/USGS.

In a paper published in the journal Ecology in July 2014, Jayna DeVore of the Warnell School of Forestry and Natural Resources at the University of Georgia and the School of Biological Sciences at the University of Sydney, and John Maerz, also of the Warnell School of Forestry and Natural Resources, describe the results of a series of experiments designed to determine exactly how the presence of Japanese Stilt Grass affects the American Toad.

Firstly DeVore & Maerz created enclosures in four areas of woodland in Georgia State that were enclosed in a way that prevented the entrance or exit of Toads but allowed Arthropods free movement. Within these enclosures the numbers of both Toads and the various Arthropod groups were monitored. No correlation between prey species numbers and Toads was found, but Toad numbers did decline in numbers in pens where Wolf Spiders (Lycopsidae) were present in large numbers.

Wolf Spiders are large predatory Spiders that hunt by waiting in ambush for mobile prey, then running it down. Small Toads, which actively seek out prey, moving about as they forage, are particularly vulnerable to this hunting technique, as they cannot feed it they remain immobile (the Spiders do not themselves forage, and will not find stationary prey) and have no defence against the Spiders.

The Carolina Wolf Spider, Hogna carolinensis. Patrick Edwin Moran/Wikimedia Commons.

DeVore & Maerz then carried out a series of cage experiments where Toads were placed in cages with or without Japanese Stilt Grass, and Wolf Spiders (Hogna carolinensis or Hogna helluo). In cages lacking Spiders the Toads survived well, regardless of the presence of the Stilt Grass, suggesting that it does not affect the soil chemistry in a way that harms the Toads. However in cages with Wolf Spiders the Toads suffered significant mortality, and this rose sharply in cages where both Spiders and Grass were present, suggesting that the Grass modifies the environment in a way that makes it easier for the Spiders to hunt the Toads.

Conceptual diagram of explored mechanisms through which Microstegium vimineum invasion can affect the survival and growth of metamorphic Toads, indicating both direct (solid line) and indirect (dashed line) effects. Black arrows are used to portray connections that were altered following invasion, resulting in significant changes in depicted parameters (e.g., densities, survival rates), whereas those that were unaffected are depicted in gray (i.e., growth rates). Significant changes are also annotated with a sign indicating whether the indicated parameter was positively (+) or negatively (-) affected (as compared with adjacent, uninvaded habitats; see Appendix C for effect sizes). In summary, invasion amplified top-down pressure on toads by increasing structural complexity, which dampened the strength of a pre-existing intraguild (IGP)/cannibalistic trophic linkage among Lycosid Spiders, resulting in higher spider densities and, subsequently, lower Toad survival within invaded habitats. The potential for bottom-up effects occurred via post-invasion changes in detrital food webs, which ultimately decreased the availability of edible invertebrates, but Toad growth was unaffected by these reductions. Although we also documented significant changes in abiotic habitat parameters following invasion, these effects alone did not significantly influence Toad survival (linkage not pictured). DeVore & Maerz (2014).