Lessons from a natural experiment: Allopatric morphological divergence and sympatric diversification in the Midas cichlid species complex are largely influenced by ecology in a deterministic way

Explaining why some lineages diversify while others do not and how are key objectives in evolutionary biology. Young radiations of closely related species derived from the same source population provide an excellent opportunity to disentangle the relative contributions of possible drivers of diversification. In these settings, lineage‐specific effects are shared and can be ruled out. Moreover, the relevant demographic and ecological parameters can be estimated accurately. Midas cichlid fish in Nicaragua have repeatedly colonized several crater lakes, diverged from the same source populations, and, interestingly, diversified in some of them but not others. Here, using the most comprehensive molecular and geometric morphometric data set on Midas cichlids to date (∼20,000 SNPs, 12 landmarks, ∼700 individuals), we aim to understand why and how crater lake populations diverge and why some of them are more prone to diversify in sympatry than others. Taking ancestor‐descendant relationships into account, we find that Midas cichlids diverged in parallel from their source population mostly—but not exclusively—by evolving more slender body shapes in all six investigated crater lakes. Admixture among crater lakes has possibly facilitated this process in one case, but overall, admixture and secondary waves of colonization cannot predict morphological divergence and intralacustrine diversification. Instead, morphological divergence is larger the more dissimilar a crater lake is compared to the source lake and happens rapidly after colonization followed by a slow‐down with time. Our data also provide some evidence that founder effects may positively contribute to divergence. The depth of a crater lake is positively associated with variation in body shapes (and number of species), presumably by providing more ecological opportunities. In conclusion, we find that parallel morphological divergence in allopatry and the propensity for diversification in sympatry across the entire Midas cichlid fish radiation is partly predictable and mostly driven by ecology.publishe

Considerations of Efficiency and Distributive Justice in Multidimensional Poverty Measurement

Ab den 1980er Jahren entwickelte Amartya Sen eine neue Wohlfahrtstheorie: den Capability Approach (Sen, 1979; 1985; 1992; 1999; 2009). Dabei ersetzen Capabilities und Functionings, d.h. das, was Personen tatsächlich in der Lage sind zu tun und zu sein, den traditionellen Einkommensansatz. Armut ist im Capability Approach das Unvermögen, ein bestimmtes Minimum an zentralen Capabilities zu erreichen, die benötigt werden, um das Leben nach den eigenen Vorstellungen zu gestalten. Der Capability Approach hat so viele interessante Eigenschaften, besonders in Bezug auf die Armutsmessung, dass er zunehmend Einfluss in der Wohlfahrtsökonomie gewinnt. Diese Entwicklung wird durch empirische Untersuchungen gefördert, die zeigen, dass dieser multidimensionale Ansatz zur Armutsmessung deutlich andere Ergebnisse generiert als der traditionelle Einkommensansatz (vgl. Klasen, 2000, Alkire und Santos, 2010, Figari, 2012). Der derzeitige multidimensionale Ansatz hat jedoch eine methodische Schwäche: Ungleichheit zwischen Armutsdimensionen wird entweder als Korrelationssensitivität definiert – womit Effizienz aber nicht Verteilungsgerechtigkeit berücksichtigt wird – oder als die Verteilung multipler Mangelerscheinungen in einer Gesellschaft – womit Verteilungsgerechtigkeit aber nicht Effizienz berücksichtigt wird. Die ersten beiden Kapitel dieser Dissertation widmen sich der Behebung dieser methodischen Schwäche. Dazu wird Ungleichheit zwischen Dimensionen zunächst als „korrelationssensitive Verteilung multipler Mangelerscheinungen in einer Gesellschaft“ definiert. Die ersten beiden Kapitel operationalisieren diese erweiterte Definition für den Fall ordinaler und kardinaler Armutsindices. Im Einzelnen wird ein neues Axiom für den ordinalen sowie den kardinalen Fall eingeführt, das das Ausmaß, mit dem ein Ungleichheitsfördernder Tausch Armut sinken (oder steigen) lässt, von der Beziehung zwischen den Armutsdimensionen abhängig macht. Diese Neuerung wird benutzt um eine neue Klasse ordinaler bzw. kardinaler Armutsindices herzuleiten. Diese zwei Klassen sind die ersten additiven Armutsindices die in der Lage sind, sowohl Ungleichheit als auch Korrelationssensitivität zu erfassen. Das dritte Kapitel nutzt das deutsche sozio-ökonomische Panel um zwei ordinale Armutsindices für Deutschland vorzuschlagen, die auf der zuvor entwickelten Methode basieren: den „Deutschen Korrelationssensitiven Armutsindex“ und den „Subjektiven Korrelationssensitiven Armutsindex“. Die beiden Indices werden mit dem offiziellen deutschen Armutsmaß, der Armutsgefährdungsquote, über Dimensionen, Regionen und über die Zeit hinweg verglichen. Die Resultate zeigen vor allem eines: die signifikanten Unterschiede in der Beurteilung von Armut und Armutstrends die durch die verschiedenen Indices versursacht werden und den hohen Mehrwert den die Operationalisierung des Capability Approachs darstellt

Genetic stock identification of Atlantic salmon (Salmo salar) populations in the southern part of the European range

notes: PMCID: PMC2882343© 2010 Griffiths et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Anadromous migratory fish species such as Atlantic salmon (Salmo salar) have significant economic, cultural and ecological importance, but present a complex case for management and conservation due to the range of their migration. Atlantic salmon exist in rivers across the North Atlantic, returning to their river of birth with a high degree of accuracy; however, despite continuing efforts and improvements in in-river conservation, they are in steep decline across their range. Salmon from rivers across Europe migrate along similar routes, where they have, historically, been subject to commercial netting. This mixed stock exploitation has the potential to devastate weak and declining populations where they are exploited indiscriminately. Despite various tagging and marking studies, the effect of marine exploitation and the marine element of the salmon lifecycle in general, remain the "black-box" of salmon management. In a number of Pacific salmonid species and in several regions within the range of the Atlantic salmon, genetic stock identification and mixed stock analysis have been used successfully to quantify exploitation rates and identify the natal origins of fish outside their home waters - to date this has not been attempted for Atlantic salmon in the south of their European range.European Union INTERREG IIIB programme (Atlantic Salmon Arc Project [ASAP], Project No. 040)

Two fish in a pod. Mislabelling on board threatens sustainability in mixed fisheries

Accuracy in reporting captures is a key element to achieve fisheries sustainability. However, identification of the catches might be a challenge when two or more species are morphologically similar and caught jointly, like the mixed fisheries of black hakes in East Atlantic African waters. Black hakes (Merluccius senegalensis and M. polli) are tough to differentiate without previous training due to their high morphological resemblance. The two species are managed as a single stock, although the biological differences between them suggest the need of a separate management. In this study, a total of 806 black hakes were visually identified by fishers on deck of fishing vessels operating in Mauritania and Senegal waters, then assigned to a species by sequencing 450bp of the Mitochondrial Control Region. Comparing the results with visual identification we found 31.4% of the total catch were incorrectly labelled on board by the fishermen. The accuracy of the fishers' identification depended on the depth of capture and on fish size, larger individuals caught from deeper waters being more correctly assigned to M. polli. Mislabelling biased to M. polli suggests that M. senegalensis, already catalogued as endangered, is being underreported, which could endanger the conservation of this species and threaten the sustainability of black hake fisheries. Our results highlight the need for separate evaluation of the stocks in mixed fisheries for morphologically similar fish. Thus, monitoring through DNA barcoding in the very first step of the seafood chain surveys would improve accurate species delimitation and reduce its impact on the correct assessment of the stocks.info:eu-repo/semantics/publishedVersio

Estructura genética de poblaciones de merluzas americanas y trazabilidad de productos pesqueros

La falta de barreras al flujo génico es característica en la mayoría de los ambientes habitados por los peces pelágicos marinos, por lo tanto se espera que las especies de peces marinos con gran capacidad de dispersión constituyan poblaciones más o menos panmícticas. Sin embargo, existe un número creciente de estudios que evidencian estructuración espacial en poblaciones de peces marinos. Durante las últimas décadas, uno de las principales retos de la genética en pesquerías ha sido la delimitación de los stocks (unidad clave para el manejo sostenible de las pesquerías). De este modo, una descripción detallada de la estructura poblacional es crucial para la conservación de los recursos naturales. A pesar que las merluzas se encuentran entre las especies de peces marinos comercialmente más explotadas, no existe demasiada información acerca de la estructura genética poblacional de las mismas. El objetivo principal de esta tesis fue evaluar la estructura genética poblacional de diferentes especies de merluzas americanas explotadas comercialmente, empleando tanto marcadores nucleares como mitocondriales. Otro de los objetivos de este trabajo fue el desarrollo de nuevos marcadores moleculares que permitieran distinguir las distintas especies de merluzas del género Merluccius, para ser aplicados en la detección de errores en la identificación de productos comerciales de merluzas. Se ha detectado un alto grado de hibridación introgresiva de tipo bidireccional, empleando microsatélites como marcadores moleculares, entre las dos especies de merluzas norteamericanas Merluccius albidus y M. bilinearis en el área de solapamiento entre sus rangos de distribución. A partir del desarrollo de nuevos marcadores microsatélites, se identificó los distintos patrones de estructuración genética poblacional en las especies de merluzas estudiadas, asociados con diferentes tipos de barreras al flujo génico. Se encontró una gran diferenciación genética entre poblaciones distantes de la merluza austral (M. australis) que habitan Nueva Zelanda y Sudamérica, probablemente asociada con corrientes que previenen la homogeneización entre las poblaciones. Diferencias genéticas sutiles, con la identificación de stocks singulares en las merluzas que habitan los golfos, han sido detectadas para M. hubbsi y M. bilinearis en el Atlántico Sur y Norte, respectivamente. El flujo génico asimétrico detectado entre los golfos y las poblaciones de mar abierto, indica que las poblaciones que habitan los golfos podrían estar actuando como fuente de variación genética para estas especies de merluzas. Finalmente, se encontró una variación genética reducida en el Océano Pacífico para Merluccius australis y Macruronus magellanicus, que podría estar asociado con una mayor explotación pesquera en esta área durante las últimas décadas. En el caso de Merluccius australis, se encontró una diferenciación significativa y un flujo génico asimétrico entre las poblaciones del océano Pacífico y el Atlántico. Se han podido identificar once especies del género Merluccius mediante la utilización de un nuevo marcador molecular basado en SNPs mitocondriales (mtSNPs). Se detectó un elevado nivel de error en la identificación de productos comerciales y desembarcos de merluzas, principalmente en especies que son explotadas de forma conjunta

Species-specific differences in adaptive phenotypic plasticity in an ecologically relevant trophic trait : hypertrophic lips in midas cichlid fishes

The spectacular species richness of cichlids and their diversity in morphology, coloration, and behavior have made them an ideal model for the study of speciation and adaptive evolution. Hypertrophic lips evolved repeatedly and independently in African and Neotropical cichlid radiations. Cichlids with hypertrophic lips forage predominantly in rocky crevices and it has been hypothesized that mechanical stress caused by friction could result in larger lips through phenotypic plasticity. To test the influence of the environment on the size and development of lips, we conducted a series of breeding and feeding experiments on Midas cichlids. Full-sibs of Amphilophus labiatus (thick-lipped) and Amphilophus citrinellus (thin-lipped) each were split into a control group which was fed food from the water column and a treatment group whose food was fixed to substrates. We found strong evidence for phenotypic plasticity on lip area in the thick-lipped species, but not in the thin-lipped species. Intermediate phenotypic values were observed in hybrids from thick- and thin-lipped species reared under “control” conditions. Thus, both a genetic, but also a phenotypic plastic component is involved in the development of hypertrophic lips in Neotropical cichlids. Moreover, species-specific adaptive phenotypic plasticity was found, suggesting that plasticity is selected for in recent thick-lipped species

Data from: Species-specific differences in adaptive phenotypic plasticity in an ecologically relevant trophic trait: hypertrophic lips in Midas cichlid fishes

The spectacular species richness of cichlids and their diversity in morphology, coloration, and behaviour have made them an ideal model for the study of speciation and adaptive evolution. Hypertrophic lips evolved repeatedly and independently in African and Neotropical cichlid radiations. Cichlids with hypertrophic lips forage predominantly in rocky crevices and it has been hypothesized that mechanical stress caused by friction could result in larger lips through phenotypic plasticity. To test the influence of the environment on the size and development of lips, we conducted a series of breeding and feeding experiments on Midas cichlids. Full-sibs of Amphilophus labiatus (thick-lipped) and A. citrinellus (thin-lipped) each were split into a control group which was fed food from the water column and a treatment group whose food was fixed to substrates. We found strong evidence for phenotypic plasticity on lip area in the thick-lipped species, but not in the thin-lipped species. Intermediate phenotypic values were observed in hybrids from thick- and thin-lipped species reared under “control” conditions. Thus, both a genetic, but also a phenotypic plastic component is involved in the development of hypertrophic lips in Neotropical cichlids. Moreover, species-specific adaptive phenotypic plasticity was found, suggesting that plasticity is selected for in recent thick-lipped species

Multispecies Outcomes of Sympatric Speciation after Admixture with the Source Population in Two Radiations of Nicaraguan Crater Lake Cichlids

The formation of species in the absence of geographic barriers (i.e. sympatric speciation) remains one of the most controversial topics in evolutionary biology. While theoretical models have shown that this most extreme case of primary divergence-with-gene-flow is possible, only a handful of accepted empirical examples exist. And even for the most convincing examples uncertainties remain; complex histories of isolation and secondary contact can make species falsely appear to have originated by sympatric speciation. This alternative scenario is notoriously difficult to rule out. Midas cichlids inhabiting small and remote crater lakes in Nicaragua are traditionally considered to be one of the best examples of sympatric speciation and lend themselves to test the different evolutionary scenarios that could lead to apparent sympatric speciation since the system is relatively small and the source populations known. Here we reconstruct the evolutionary history of two small-scale radiations of Midas cichlids inhabiting crater lakes Apoyo and Xiloá through a comprehensive genomic data set. We find no signs of differential admixture of any of the sympatric species in the respective radiations. Together with coalescent simulations of different demographic models our results support a scenario of speciation that was initiated in sympatry and does not result from secondary contact of already partly diverged populations. Furthermore, several species seem to have diverged simultaneously, making Midas cichlids an empirical example of multispecies outcomes of sympatric speciation. Importantly, however, the demographic models strongly support an admixture event from the source population into both crater lakes shortly before the onset of the radiations within the lakes. This opens the possibility that the formation of reproductive barriers involved in sympatric speciation was facilitated by genetic variants that evolved in a period of isolation between the initial founding population and the secondary migrants that came from the same source population. Thus, the exact mechanisms by which these species arose might be different from what had been thought before.publishe

Pronounced genetic differentiation of small, isolated and fragmented tilapia populations inhabiting the Magadi Soda Lake in Kenya

Lake Magadi, an alkaline hypersaline lake in Kenya, is one of the most extreme water bodies known. Although its water temperatures often exceed 40°C, a particular lineage of ‘dwarf’ tilapia, Alcolapia grahami, has evolved remarkable adaptations to survive in this hostile environment. Magadi tilapia exists in small fragmented populations in isolated lagoons within Lake Magadi and its satellite Lake, Little Magadi. In spite of the potential this tilapia holds for understanding evolutionary processes in stressful environments, few genetic studies have focused on this species. We examined the genetic diversity and spatial genetic relationships of Magadi tilapia populations using microsatellite and mitochondrial markers. High levels of genetic variation were found to be supporting the hypothesis that A. grahami populations represent remnants of a much larger fish population that inhabited paleo-lake Orolonga. In contrast to previous studies, we found a well-supported genetic structure of A. grahami consisting of three differentiated genetic clusters (a) Little Magadi, (b) Fish Spring Lagoon and (c) Rest of Magadi. Given the importance of this species to the Magadi ecosystem and its potential evolutionary significance, the three genetic clusters should be considered as separate gene pools and conservation strategies aimed at protecting the species based on these clusters are recommended