"Nested" cryptic diversity in a widespread marine ecosystem engineer: a challenge for detecting biological invasions

<p>Abstract</p> <p>Background</p> <p>Ecosystem engineers facilitate habitat formation and enhance biodiversity, but when they become invasive, they present a critical threat to native communities because they can drastically alter the receiving habitat. Management of such species thus needs to be a priority, but the poorly resolved taxonomy of many ecosystem engineers represents a major obstacle to correctly identifying them as being either native or introduced. We address this dilemma by studying the sea squirt <it>Pyura stolonifera</it>, an important ecosystem engineer that dominates coastal communities particularly in the southern hemisphere. Using DNA sequence data from four independently evolving loci, we aimed to determine levels of cryptic diversity, the invasive or native status of each regional population, and the most appropriate sampling design for identifying the geographic ranges of each evolutionary unit.</p> <p>Results</p> <p>Extensive sampling in Africa, Australasia and South America revealed the existence of "nested" levels of cryptic diversity, in which at least five distinct species can be further subdivided into smaller-scale genetic lineages. The ranges of several evolutionary units are limited by well-documented biogeographic disjunctions. Evidence for both cryptic native diversity and the existence of invasive populations allows us to considerably refine our view of the native versus introduced status of the evolutionary units within <it>Pyura stolonifera </it>in the different coastal communities they dominate.</p> <p>Conclusions</p> <p>This study illustrates the degree of taxonomic complexity that can exist within widespread species for which there is little taxonomic expertise, and it highlights the challenges involved in distinguishing between indigenous and introduced populations. The fact that multiple genetic lineages can be native to a single geographic region indicates that it is imperative to obtain samples from as many different habitat types and biotic zones as possible when attempting to identify the source region of a putative invader. "Nested" cryptic diversity, and the difficulties in correctly identifying invasive species that arise from it, represent a major challenge for managing biodiversity.</p

Global Diversity of Ascidiacea

The class Ascidiacea presents fundamental opportunities for research in the fields of development, evolution, ecology, natural products and more. This review provides a comprehensive overview of the current knowledge regarding the global biodiversity of the class Ascidiacea, focusing in their taxonomy, main regions of biodiversity, and distribution patterns. Based on analysis of the literature and the species registered in the online World Register of Marine Species, we assembled a list of 2815 described species. The highest number of species and families is found in the order Aplousobranchia. Didemnidae and Styelidae families have the highest number of species with more than 500 within each group. Sixty percent of described species are colonial. Species richness is highest in tropical regions, where colonial species predominate. In higher latitudes solitary species gradually contribute more to the total species richness. We emphasize the strong association between species richness and sampling efforts, and discuss the risks of invasive species. Our inventory is certainly incomplete as the ascidian fauna in many areas around the world is relatively poorly known, and many new species continue to be discovered and described each year

Technical Terms of Reference: Name: Mr X Tofu

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Effect of seed rate and irrigation level on the performance of wheat cv. Gourab

The effect of seed rate and irrigation level on the performance of wheat cv. Gourab was studied. The experiment comprises of two factors namely (1) four seed rate viz. 100, 120, 140 and 160 kgha-1 and (2) four levels of irrigation namely (i) no irrigation i.e. control, (ii) one irrigation given at Crown root initiation (CRI) stage, (iii) two irrigations given at CRI and Panicle initiation stages and (iv) three irrigation given at CRI, panicle initiation and grain filling stages. All of the yields contributing characters were significantly affected by seed rate except 1000-grain weight. The highest plant height (82.36 cm), total tillers plant-1(8.99), effective tillers plant-1(3.49) , spike length (8.05 cm), spikelets spike-1 (15.50), filled grain spike-1 (31.05), grain yield (2.82 t ha-1), straw yield (3.73 t ha-1), biological yield (6.55 t ha-1) and harvest index (42.43%) were recorded from the seed rate of 140 kg ha-1. Most of the yields contributing characters were significant due to effect of irrigation level. The highest plant height (82.33 cm), spike length (8.37 cm), filled grain spike-1 (31.90), effective tillers plant-1 (3.31), grain yield (3.30 t ha-1), straw yield (4.09 t ha-1), biological yield(7.39 t ha-1) and harvest index (44.47%) were recorded when one irrigation given at CRI stage . The interaction between seed rate and irrigation level influenced significantly all the plant characters except plant height, spikelets spike-1 and 1000-grains weight. The highest spike length (8.63 cm), grain yield (3.70 t ha-1), biological yield (8.06 t ha-1) and harvest index (45.91%) were found from the seed rate of 140 kg ha-1 combined with one irrigation applied at CRI stage. So it may be stated that the seed rate of 140 kg ha-1 with one irrigation given at CRI stage may be practiced for better performance of wheat cv. Gourab. Keyword: Seed rate; Irrigation level; Gourab DOI: 10.3329/jbau.v7i1.4797 J. Bangladesh Agril. Univ. 7(1): 47-52, 2009</jats:p

As the candidate’s co-supervisor I have approved this dissertation for submission.

Opgedra aan my ma, Georgina, vir al haar liefde en ondersteuning. This document was created in LATEX 2ε ii As the candidate’s supervisor I have approved this dissertation for submission