Infrequent Migration Research Articles

A tipping point in parapatric speciation

More than two loci are involved in reproductive isolation in most cases of putative recent speciation. We study the speciation between two geographically isolated populations connected by infrequent migration, in which incompatibility is controlled by quantitative loci. Incompatibility genetic distance is defined as the fraction of compatibility controlling loci that are different between individuals. Speciation is established when genetic distance reaches a threshold level in spite of occasional migration and subsequent hybridization that reduce genetic distance. With stochastic analysis, we investigate how the time to speciation depends on the manner in which the magnitude of incompatibility increases with genetic distance. Results are: (1) The time to speciation is short if the migration rate is smaller than the mutation rate, or if intermediate levels of genetic distance cause mild incompatibility, making migrants less effective in reducing genetic distance. (2) Genetic distance may fluctuate around a positive quasi-equilibrium level for a long time, and suddenly show a quick passage to speciation when it goes beyond a “tipping point.” Notably a gradual increase in incompatibility can result in a sudden and rapid formation of a new species. (3) Speciation becomes very slow if incompatibility is effective for individuals differing at only one locus. These findings provide testable predictions on reproductive traits controlled by specific incompatibility accumulation forms that facilitate the speciation process.

Smallness of the number of incompatibility loci can facilitate parapatric speciation

We studied the time to speciation by geographic isolation for a species living on two islands connected by infrequent migration. Assumptions were that incompatibility was controlled by a finite number of quantitative loci, and individuals differing in loci of more than some threshold fraction do not mix genetically with each other. We also assumed sexual haploid species, each population being nearly monomorphic, and free recombination between loci for within-population processes. The genetic distance (defined as the fraction of loci differing between populations) followed stochastic processes, which were analyzed by means of stochastic differential equations, diffusion equations, and individual-based simulations. The distance increases by the accumulation of novel mutations but decreases by migration and hybridization. It may converge to a quasi-equilibrium around which it fluctuates thereafter. If the threshold fraction of speciation is controlled, the smallness of the number of incompatibility loci enhanced the magnitude of fluctuation around the quasi-equilibrium and shortened the time to speciation considerably. Novel species were created by mutation accumulation and repeated infrequent migration, and the rate of species creation was the fastest for an intermediate rate of migration. A smaller number of loci increased the optimal migration rate and the species creation rate.

Reproductive interference can promote recurrent speciation

AbstractMany consequences of reproductive interference have important implications in biodiversity conservation policy. After briefly summarizing our comments on the articles in this special feature, we focus on the role of reproductive interference in speciation due to geographic isolation with only infrequent migration between islands (or island‐like habitats). As two isolated populations accumulate incompatible genes, they became genetically distinct. When a rare migration occurs from one island to the other, reproductive interference greatly affects its outcome. A paper in this special feature showed that either the migrant or resident population becomes extinct, presumably due to reproductive interference. However, we also found cases in which the migrant and resident populations evolved quickly to avoid mixing, either by character displacement or spatial segregation within the island. To improve our understanding of the dynamics of species diversity, theoretical modeling and empirical studies of reproductive interference immediately after invasion are important targets for future studies.

First passage time to allopatric speciation

Allopatric speciation is a mechanism to evolve reproductive isolation; it is caused by the accumulation of genetic differences between populations while they are geographically isolated. Here, we studied a simple stochastic model for the time until speciation caused by geographical isolation in fragmented populations that experience recurrent but infrequent migration between subpopulations. We assumed that mating incompatibility is controlled by a number of loci that behave as neutral characters in the accumulation of novel mutations within each population. Genetic distance between populations was defined as the number of incompatibility-controlling loci that differ between them. Genetic distance increases through the separate accumulation of mutations in different populations, but decreases after a successful migration event followed by genetic mixing between migrants and residents. We calculated the time to allopatric speciation, which occurs when the genetic distance exceeds a specified threshold. If the number of invasive individuals relative to the resident population is not very large, diffusion approximation provides an accurate prediction. There is an intermediate optimal rate of migration that maximizes the rate of species creation by recurrent invasion and diversification. We also examined cases that involved more than two populations.

Perspectives for the lionfish invasion in the South Atlantic: Are Brazilian reefs protected by the currents?

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 485:1-7 (2013) - DOI: https://doi.org/10.3354/meps10383 FEATURE ARTICLE: AS WE SEE IT Perspectives for the lionfish invasion in the South Atlantic: Are Brazilian reefs protected by the currents? Osmar J. Luiz1,*, Sergio R. Floeter2, Luiz A. Rocha3, Carlos E. L. Ferreira4 1Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109, Australia 2Departamento de Ecologia e Zoologia, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina 88040-900, Brazil 3Section of Ichthyology, California Academy of Sciences, San Francisco, California 94118, USA 4Departamento de Biologia Marinha, Universidade Federal Fluminense, Niterói, Rio de Janeiro 24001-970, Brazil *Email: osmar.luiz-jr@mq.edu.au ABSTRACT: The Indo-Pacific lionfish species Pterois volitans and P. miles are piscivorous predators that were introduced probably via aquarium release to the northwestern Atlantic approximately 15 yr ago and rapidly spread and established through the Greater Caribbean. Possible ecological impacts of this invasion on native species are a legitimate cause for concern. Despite predictions that lionfishes will extend their range throughout most of the eastern coast of South America, they are yet to be recorded in Brazil. We present a perspective analysis of the lionfish invasion in the southwestern Atlantic by investigating patterns of fish species movement across the Amazon-Orinoco plume (AOP), a large freshwater and sediment runoff between the Caribbean and the Brazilian Provinces that represents a ‘porous’ barrier to dispersal for reef organisms. We analyzed records of species that have recently crossed the barrier and found that the Brazilian Province contributes a significantly higher proportion of its endemic fauna to the pool of crossers, indicating that movements of vagrant species across the AOP are more common from Brazil towards the Caribbean than vice versa. Nevertheless, despite infrequent migration southwards against the currents, our analysis indicates that such migration has occurred historically and has resulted in the establishment of new populations. Our analysis indicates that a combination of the effects of the AOP and prevailing currents along northern Brazil may slow the pace of the potential invasion, which could help eradication programs if action is taken before lionfishes become widespread and established in Brazil. KEY WORDS: Amazon-Orinoco barrier · Exotic species · Reef fish · North Brazil Current · Vagrant · Pterois Full text in pdf format Information about this Feature Article NextCite this article as: Luiz OJ, Floeter SR, Rocha LA, Ferreira CEL (2013) Perspectives for the lionfish invasion in the South Atlantic: Are Brazilian reefs protected by the currents?. Mar Ecol Prog Ser 485:1-7. https://doi.org/10.3354/meps10383 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 485. Online publication date: June 27, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

PHYLOGEOGRAPHY AND POPULATION STRUCURE OF AEDES AEGYPTI IN ARIZONA

Aedes aegypti, the mosquito responsible for transmitting dengue, has colonized many cities and towns throughout Arizona. Determining both the migration between, and the origin of, local Ae. aegypti populations is important for vector control and disease prevention purposes. Amplified fragment length polymorphism was used to infer geographic structure and local substructure, and effective migration rates (M, migrants per generation) between populations, and to determine genetic differentiation between populations (PhiPT). Three geographically and genetically differentiated groups of populations were identified. Population substructure was only detected in the border town of Nogales. Reliable estimates of M between regions ranged from 1.02 to 3.41 and between cities within regions from 1.66 to 4.44. In general, pairwise PhiPT were lowest between cities within regions. The observed patterns of genetic differentiation suggest infrequent migration between populations and are compatible with the idea of human transport facilitating dispersal between regions.

From individual behavior to metapopulation dynamics: unifying the patchy population and classic metapopulation models.

Spatially structured populations in patchy habitats show much variation in migration rate, from patchy populations in which individuals move repeatedly among habitat patches to classic metapopulations with infrequent migration among discrete populations. To establish a common framework for population dynamics in patchy habitats, we describe an individual-based model (IBM) involving a diffusion approximation of correlated random walk of individual movements. As an example, we apply the model to the Glanville fritillary butterfly (Melitaea cinxia) inhabiting a highly fragmented landscape. We derive stochastic patch occupancy model (SPOM) approximations for the IBMs assuming pure demographic stochasticity, uncorrelated environmental stochasticity, or completely correlated environmental stochasticity in local dynamics. Using realistic parameter values for the Glanville fritillary, we show that the SPOMs mimic the behavior of the IBMs well. The SPOMs derived from IBMs have parameters that relate directly to the life history and behavior of individuals, which is an advantage for model interpretation and parameter estimation. The modeling approach that we describe here provides a unified framework for patchy populations with much movements among habitat patches and classic metapopulations with infrequent movements.

From Individual Behavior to Metapopulation Dynamics: Unifying the Patchy Population and Classic Metapopulation Models

Spatially structured populations in patchy habitats show much variation in migration rate, from patchy populations in which individuals move repeatedly among habitat patches to classic metapopulations with infrequent migration among discrete populations. To establish a common framework for population dynamics in patchy habitats, we describe an individual‐based model (IBM) involving a diffusion approximation of correlated random walk of individual movements. As an example, we apply the model to the Glanville fritillary butterfly (Melitaea cinxia) inhabiting a highly fragmented landscape. We derive stochastic patch occupancy model (SPOM) approximations for the IBMs assuming pure demographic stochasticity, uncorrelated environmental stochasticity, or completely correlated environmental stochasticity in local dynamics. Using realistic parameter values for the Glanville fritillary, we show that the SPOMs mimic the behavior of the IBMs well. The SPOMs derived from IBMs have parameters that relate directly to the life history and behavior of individuals, which is an advantage for model interpretation and parameter estimation. The modeling approach that we describe here provides a unified framework for patchy populations with much movements among habitat patches and classic metapopulations with infrequent movements.

Mate choice in the face of both inbreeding and outbreeding depression in the intertidal copepod Tigriopus californicus

In species vulnerable to both inbreeding and outbreeding depression, individuals might be expected to choose mates at intermediate levels of genetic relatedness. Previous work on the intertidal copepod Tigriopus californicus has repeatedly shown that crosses between populations result in either no effect or hybrid vigor in the first generation, and hybrid breakdown in the second generation. Previous work also shows that mating between full siblings results in inbreeding depression. The present study again found inbreeding depression, with full sibling mating causing significant fitness declines in two of the three populations assayed. In the mate choice assays, a single female was combined with two males. Despite the costs of both inbreeding and outbreeding, mate choice showed clear inbreeding avoidance but no clear pattern of outbreeding avoidance. This lack of outbreeding avoidance may be attributed either to the temporary increase in fitness in the F1 generation or to the absence of selection for premating isolation in wholly allopatric populations with infrequent migration. If this inability to avoid unwise matings is common to other taxa, it may contribute to the problem of outbreeding depression when allopatric populations are mixed together.

Traffic-based performance comparison of mobile support strategies

This paper presents performance comparison among five strategies for mobile support. The major facilities that are required for a network protocol to support mobile hosts are location management and packet forwarding. Based on this obser- vation, we consider five basic strategies which use distinct methods to achieve these facilities and compare their performance. These five strategies are Broadcast Notification (BN), Broadcast Forwarding (BF), Broadcast Query (BQ), Default Forwarding (DF), and Default Query (DQ). As a result of analytical evaluation and comparison, it is shown that under different network con- ditions, such as number of routers, network topology, migration/communication ratio, data/control packet size ratio, different strategies produce minimum network traffic. In short, DF and DQ show the best performance in network size scaling, while BF and BQ are efficient for frequent migration. On the other hand, BN is suitable for a small network which has hosts with infrequent migration.