3,506 research outputs found
Tracking Invasion Histories in the Sea: Facing Complex Scenarios Using Multilocus Data
No full textIn recent years, new analytical tools have allowed researchers to extract historical information contained in molecular data, which has fundamentally transformed our understanding of processes ruling biological invasions. However, the use of these new analytical tools has been largely restricted to studies of terrestrial organisms despite the growing recognition that the sea contains ecosystems that are amongst the most heavily affected by biological invasions, and that marine invasion histories are often remarkably complex. Here, we studied the routes of invasion and colonisation histories of an invasive marine invertebrate Microcosmus squamiger (Ascidiacea) using microsatellite loci, mitochondrial DNA sequence data and 11 worldwide populations. Discriminant analysis of principal components, clustering methods and approximate Bayesian computation (ABC) methods showed that the most likely source of the introduced populations was a single admixture event that involved populations from two genetically differentiated ancestral regions - the western and eastern coasts of Australia. The ABC analyses revealed that colonisation of the introduced range of M. squamiger consisted of a series of non-independent introductions along the coastlines of Africa, North America and Europe. Furthermore, we inferred that the sequence of colonisation across continents was in line with historical taxonomic records - first the Mediterranean Sea and South Africa from an unsampled ancestral population, followed by sequential introductions in California and, more recently, the NE Atlantic Ocean. We revealed the most likely invasion history for world populations of M. squamiger, which is broadly characterized by the presence of multiple ancestral sources and non-independent introductions within the introduced range. The results presented here illustrate the complexity of marine invasion routes and identify a cause-effect relationship between human-mediated transport and the success of widespread marine non-indigenous species, which benefit from stepping-stone invasions and admixture processes involving different sources for the spread and expansion of their range
Phylogeography of the widespread marine invader Microcosmus squamiger (Ascidiacea) reveals high genetic diversity of introduced populations and non-independent colonizations
No full textThe spread of non-indigenous species into new marine habitats represents an increasing threat to global diversity. Genetic techniques provide basic understanding of the invasion processes. The ascidian Microcosmus squamiger is considered to be native to Australia, having been spread worldwide via transoceanic vessels. It has successfully invaded artificial and natural habitats where it has become a pest. We studied phylogeography and genetic structure of 12 M. squamiger populations, including samples from its native range (Australia) and introduced populations from the Indian, Pacific, and Atlantic oceans, as well as the Mediterranean Sea. We amplified 574 bp of the mitochondrial COI gene in 258 individuals and found a total of 52 haplotypes. A haplotype tree revealed two main groups of haplotypes. The relative frequency of each group of haplotypes, multidimensional scaling, and analysis of molecular variance showed important differences between the western Australia localities and the remaining ones (eastern Australia and introduced populations). Furthermore, we found that the colonization of the different areas by M. squamiger has not occurred independently, as many introduced populations shared some low frequency alleles. A nested clade analysis showed a global pattern of restricted gene flow with isolation by distance, although we found episodes of long-distance dispersal in some clades. A contiguous range expansion was detected between Australian populations. We conclude that M. squamiger is native to Australia and has most likely expanded its range of distribution sequentially through worldwide shipping, especially from the harbours of the more populated eastern Australia. In introduced populations, we found a high genetic diversity which suggests enhanced invasive potential. Consequently, there is a need to control this species, as it outcompetes local biota and is an economic threat
Population dynamics and life cycle of the introduced ascidian Microcosmus squamiger in the Mediterranean Sea
No full textMarine introductions are a serious threat for biodiversity, especially in seas where shipping is intensive. Microcosmus squamiger is a widespread marine invader that can alter native biota and it is therefore imperative to understand its biology and ecology. We studied the population dynamics and reproductive cycles of M. squamiger over a 2-year period, as well as its settlement and colonization patterns, in a north-western Mediterranean (NE Spain) locality where M. squamiger has been introduced. All biological parameters showed a strong seasonal pattern that peaked in summer with a major spawning episode at the end of summer. Size-frequency histograms indicated a 2-year cycle. Colonization experiments suggested that M. squamiger recruitment mortality is high and requires a well structured community. In addition, we monitored the abundance of the native predator Thais haemastoma, which showed a significant positive correlation with M. squamiger biomass, indicating its potential usefulness as a biological control
Polyzoa iosune Turon & Lopez-Legentil
No full textPolyzoa iosune Turon & López-Legentil Fig. 10 Localities: 6 N. Holotype: a colony has been designated as the holotype and deposited in the Museo Nacional de Historia Natural de Chile (code MNHNCL TUN- 15001). Two other colonies (paratypes) are kept at the Biological Collections Room of the Universidad Católica del Norte (SCBUCN 3962). Several colonies of this new species have been found in the lower intertidal in the Coquimbo area. They form thick carpets by the union side by side of elongated zooids, reaching 17 mm in height. A single colony may cover hundreds of square centimetres. The tunic is of a clear brownish colour, and the siphons are pigmented in red. Small zooids appear in between larger ones, attached to their tunics. Thick stolons are found at the basis of the colony. The tunic is thin but firm. The zooids have a weekly muscular body wall that allows the observation of some internal features. There is an inner oral velum and about 16 tentacles (big and medium size). The aperture of the neural gland is oval-vertical. There are 7 longitudinal vessels to the right and 4 (sometimes 5) to the left. Parastigmatic vessels cut the stigmata (up to 10 per mesh). Sometimes there are 2 and even 3 parastigmatic vessels between two consecutive transverse vessels. The digestive system forms an open primary loop, with a long and straight intestine reaching anteriorly towards the atrial siphon and ending in a smooth anus. The stomach has 12–16 folds and a pyloric caecum. There are several endocarps (6–8) attached to the body wall at each side, round or elongated. Up to 18 gonads can be found on the right hand side, forming a row adjacent to the endostyle. The gonads are hermaphrodite and elongated. The male portion is basal and forms most of the gonad, and the female portion lies distally and apically. There is a short and wide oviduct opening distally with a scalloped aperture, and a long and thin subterminal spermduct. To the left there are only 5–7 hermaphrodite gonads between the endostyle and the ascending intestine. Some zooids brood larvae in the peribranchial cavity. The larval trunk length is up to 0.65 mm. When mature, the larvae feature a ring of tubular anterior ampullae (6–7 pairs), three conical adhesive papillae, and a single pigmented spot. Remarks. Monniot (1970) established a tabular key for the known species of Polyzoa. None matches the characters observed in the Chilean specimens. In particular, the number of longitudinal vessels falls within the variability of P. minor alone (Monniot 1973), a different species in terms of size, colony form, number of gonads and larval morphology. The only species featuring zooids joined together and of the size found here is P. opuntia, but it has consistently 8 longitudinal vessels per side, among other differences. On the other hand, and based on the COI sequences obtained here, P. iosune forms a well-suported clade (Neighbour Joining tree, results not shown), sister to the clade of P. opuntia sequences, with which it features 8–9 % sequence differentiation. Species described more recently such as P. e xi g ua and P. nodosa (Kott 1990), or P. atlantica (Sanamyan et al. 2009) are all clearly different in colony and zooid size and shape, as well as in internal features. Derivatio nominis: this species is dedicated to María Jesús Uriz, colleague, friend, and great sponge specialist. Iosune (María Jesús in basc language) is here used as substantive in apposition.Published as part of Turon, Xavier, Cañete, Juan I., Sellanes, Javier, Rocha, Rosana M. & López-Legentil, Susanna, 2016, Ascidian fauna (Tunicata, Ascidiacea) of subantarctic and temperate regions of Chile, pp. 151-180 in Zootaxa 4093 (2) on pages 168-169, DOI: 10.11646/zootaxa.4093.2.1, http://zenodo.org/record/26766
Spread of Microcosmus squamiger (Ascidiacea: Pyuridae) in the Mediterranean Sea and adjacent waters
No full textThe Mediterranean Sea is subject to an ever-increasing arrival of non-indigenous marine organisms. Microcosmus squamiger is a solitary ascidian that inhabits shallow rocky littoral habitats. It probably originated in Australia and it has shown great invasive potential in other parts of the world. In the Mediterranean, M. squamiger has only been reported at a few sites in Spain and Italy. However, the closely related species Microcosmus exasperatus has been reported in several areas of the western Mediterranean. As these species can be easily confused, we re-examined most of the material from previous studies and our personal collections. In addition, sampling was done at several sites along the western Mediterranean and Atlantic coasts. The results showed that the majority of the M. exasperatus reports correspond to M. squamiger, and that M. squamiger is common on the Atlantic shores. This suggests that M. squamiger has entered the Mediterranean through the Gibraltar Strait, while the restricted distribution in the eastern Mediterranean of M. exasperatus suggests that this species is probably a Lessepsian migrant. In the Mediterranean Sea, M. squamiger has the ability to occupy extensive areas of hard substrata and to outcompete native species. Further studies are necessary to assess what impacts this invasive species have on native communities
Isolation of polymorphic microsatellite loci for the marine invader Microcosmus squamiger (Ascidiacea)
No full textThe ascidian Microcosmus squamiger is native to Australia and has recently spread worldwide. It has become a pest in some littoral communities within its introduced range. An enriched genomic library of M. squamiger resulted in a total of eight polymorphic loci that were genotyped in 20 individuals from a population within its introduced range, and 20 individuals more from a native population. The mean number of alleles per locus was 5.33 and mean observed heterozygosity was 0.432. No significant linkage disequilibrium was found among loci pairs. Significant genetic differentiation was observed between populations
Tough adults, frail babies: an analysis of stress sensitivity across early life-history stages of widely introduced marine invertebrates
No full textAll ontogenetic stages of a life cycle are exposed to environmental conditions so that population persistence depends on the performance of both adults and offspring. Most studies analysing the influence of abiotic conditions on species performance have focussed on adults, while studies covering early life-history stages remain rare. We investigated the responses of early stages of two widely introduced ascidians, Styela plicata and Microcosmus squamiger, to different abiotic conditions. Stressors mimicked conditions in the habitats where both species can be found in their distributional ranges and responses were related to the selection potential of their populations by analysing their genetic diversity. Four developmental stages (egg fertilisation, larval development, settlement, metamorphosis) were studied after exposure to high temperature (30°C), low salinities (26 and 22 ) and high copper concentrations (25, 50 and 100 µg/L). Although most stressors effectively led to failure of complete development (fertilisation through metamorphosis), fertilisation and larval development were the most sensitive stages. All the studied stressors affected the development of both species, though responses differed with stage and stressor. S. plicata was overall more resistant to copper, and some stages of M. squamiger to low salinities. No relationship was found between parental genetic composition and responses to stressors. We conclude that successful development can be prevented at several life-history stages, and therefore, it is essential to consider multiple stages when assessing species' abilities to tolerate stress. Moreover, we found that early development of these species cannot be completed under conditions prevailing where adults live. These populations must therefore recruit from elsewhere or reproduce during temporal windows of more benign conditions. Alternatively, novel strategies or behaviours that increase overall reproductive success might be responsible for ensuring population survival
Phylogeography and the Description of Geographic Patterns in Invasion Genomics
No full textEste artículo contiene 6 páginas, 1 figura.Phylogeography is an integrative discipline that aims to understand the geographic ordination
of genotypes. In recent decades, phylogeographic approaches have been used to enhance our
understanding of both biogeography and landscape genetics across a variety of spatial and temporal
scales. By definition, species studied using these approaches need to meet certain assumptions
(e.g. mutation and drift need to be at equilibrium). However, artificially dispersed species (i.e.
non-indigenous, naturalised and invasive species) often do not comply with these assumptions.
Thus, the use of phylogeographic approaches to study these species may lead to erroneous
interpretations. Considering that self-denominated phylogeographic studies of invasive species
have proliferated in recent years and that genomic tools are now more accessible than ever
before, kick starting this debate is particularly timely. We argue herein that invasion scientists
must carefully use phylogeographic approaches when studying genomic data obtained from
the introduced range. In addition, the assumptions of these phylogeographic approaches need
to be explicitly considered when interpreting genomic patterns of invasive species. Finally,
we suggest abandoning the use of the term ‘phylogeography’ for describing geographically
contextualized genomic data from the introduced range to avoid both terminological and
methodological confusion.The ideas developed in this
opinion note were partly conceived during the development of
the project CTM2017-88080 (MCIU/AEI/FEDER/UE) from the
Spanish Government.Peer reviewe
FIGURE 9. Cnemidocarpa verrucosa, A in Ascidian fauna (Tunicata, Ascidiacea) of subantarctic and temperate regions of Chile
No full textFIGURE 9. Cnemidocarpa verrucosa, A, natural aspect; B, dissected body. Scale bar: A, B, 2 cm.Published as part of Turon, Xavier, Cañete, Juan I., Sellanes, Javier, Rocha, Rosana M. & López-Legentil, Susanna, 2016, Ascidian fauna (Tunicata, Ascidiacea) of subantarctic and temperate regions of Chile, pp. 151-180 in Zootaxa 4093 (2) on page 167, DOI: 10.11646/zootaxa.4093.2.1, http://zenodo.org/record/26766
Non-lethal effects of an invasive species in the marine environment: the importance of early life-history stages
No full textStudies examining the effects of invasive species have focussed traditionally on the direct/lethal effects of the invasive on the native community but there is a growing recognition that invasive species may also have non-lethal effects. In terrestrial systems, non-lethal effects of invasive species can disrupt early life-history phases (such as fertilisation, dispersal and subsequent establishment) of native species, but in the marine environment most studies focus on adult rather than early life-history stages. Here, we examine the potential for an introduced sessile marine invertebrate (Styela plicata) to exert both lethal and non-lethal effects on a native species (Microcosmus squamiger) across multiple early life-history stages. We determined whether sperm from the invasive species interfered with the fertilisation of eggs from the native species and found no effect. However, we did find strong effects of the invasive species on the post-fertilisation performance of the native species. The invasive species inhibited the settlement of native larvae and, in the field, the presence of the invasive species was associated with a ten-fold increase in the post-settlement mortality of the native species, as well as an initial reduction of growth in the native. Our results suggest that larvae of the native species avoid settling near the invasive species due to reduced post-settlement survival in its presence. Overall, we found that invasive species can have complex and pervasive effects (both lethal and non-lethal) across the early life-history stages of the native species, which are likely to result in its displacement and to facilitate further invasion
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