Ana Almodóvar

Cryptic speciation of hormogastrid earthworms revealed by mitochondrial and nuclear data.

Species delimitation of earthworms has been difficult to determine with certainty due to their structural simplicity. We sequenced fragments of COI, 16S, t-RNAs and 28S for 202 Hormogastridae individuals from the central Iberian Peninsula and three outgroup taxa. A morphological constancy was found but a high genetic diversity suggests the presence of five cryptic allopatric species. Results showed a pattern of isolation by distance and a positive but weak correlation between some soil properties (coarse sand and total loam content) and genetic distances, which indicates that these populations may have been shaped genetically but not morphologically, by the environment.

High genetic divergence of hormogastrid earthworms (Annelida, Oligochaeta) in the central Iberian Peninsula: evolutionary and demographic implications

Hormogastridae earthworms are highly important for the functioning of the Mediterranean soil system. However, little is known about the species distribution and genetic diversity of these soil invertebrates. In the present study, the genetic differentiation and gene flow were studied among populations of hormogastrids from the central Iberian Peninsula. A 648‐bp portion of the mitochondrial cytochrome c oxidase I gene was sequenced for 82 individuals from 7 localities, resulting in the identification of 38 haplotypes exclusive to localities. All of the individuals were morphologically identified as Hormogaster elisae, but the high genetic divergence found among populations (up to 20.20%) suggests the occurrence of more than one cryptic species within this region. Further analysis of the phylogenetic relationships revealed six different evolutionary lineages coincident with geographical location, including the two nearest populations Molar and Redueña as one evolutionary unit. From these results, at least three new species could be inferred, in addition to the morphospecies H. elisae s.s. Partitioning of genetic variance among populations indicated that isolation by distance was the primary agent for differentiation of the investigated hormogastrid populations. Our data suggest that the evolutionary lineages for H. elisae s.l. originated between the late Miocene and the early Pleistocene, but that mtDNA genealogies coalesce on a more recent scale of a few thousand years.

Effects of a small hydropower station upon brown trout Salmo trutta L. in the River Hoz Seca (Tagus basin, Spain) one year after regulation

A small hydroelectric power station was built in 1993 on the River Hoz Seca (Tagus basin, central Spain). Pre- and post-regulation studies provided the opportunity to test the early effects of this disturbance on the brown trout Salmo trutta L. population. Before and after comparisons of population density and biomass, age composition, growth and production were made upstream and downstream of the diversion dam. The effects of disturbance on benthic macroinvertebrates were also analysed but no changes in abundance were detected. The downstream estimated population densities and biomass of trout showed a decrease of about 50 and 43%, respectively, following regulation. Examination of length-for-age tables revealed no obvious change in growth but a significant difference in age structure. The main consequence of the imposed fluctuating flow regime was a serious reduction in trout production caused by a loss of suitable habitat and a loss of juveniles. Copyright

Growth Pattern of Stream-Dwelling Brown Trout under Contrasting Thermal Conditions

Abstract Growth of brown trout Salmo trutta was analyzed based on 3 years of simultaneous temperature and growth data from seven streams of contrasting chemical and biological character. A laboratory-based growth model was employed to examine geographical variation in growth performance among wild populations. A sensitivity analysis of model predictions was also performed based on simulated optimum temperatures for growth within the range of observed temperatures and on the optimum temperature used in the model. In spite of the diverse environmental conditions, the annual increment in body mass was not significantly different among most populations. However, the ratio of the actual growth rate to the maximum growth rate predicted by the model differed among rivers. A significant negative correlation was found between this ratio and mean annual water temperature. The growth model thus underestimated growth in the coldest rivers, suggesting that adaptations to local thermal conditions can occur at a small g...

Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.

Understanding the biogeography of a group of earthworms in the Mediterranean basin—The phylogenetic puzzle of Hormogastridae (Clitellata: Oligochaeta)

Traditional earthworm taxonomy is hindered due to their anatomical simplicity and the plasticity of the characteristics often used for diagnosing species. Making phylogenetic inferences based on these characters is more than difficult. In this study we use molecular tools to unravel the phylogeny of the clitellate family Hormogastridae. The family includes species of large to mid-sized earthworms distributed almost exclusively in the western Mediterranean region where they play an important ecological role. We analyzed individuals from 46 locations spanning the Iberian Peninsula to Corsica and Sardinia, representing the four described genera in the family and 20 species. Molecular markers include mitochondrial regions of the cytochrome c oxidase subunit I gene (COI), 16S rRNA and tRNAs for Leu, Ala, and Ser, two nuclear ribosomal genes (nearly complete 18S rRNA and a fragment of 28S rRNA) and two nuclear protein-encoding genes (histones H3 and H4). Analyses of the data using different approaches corroborates monophyly of Hormogastridae, but the genus Hormogaster is paraphyletic and Hormogaster pretiosa appears polyphyletic, stressing the need for taxonomic revisionary work in the family. The genus Vignysa could represent an early offshoot in the family, although the relationships with other genera are uncertain. The genus Hemigastrodrilus is related to the Hormogaster elisae complex and both are found in the Atlantic drainage of the Iberian Peninsula and France. From a biogeographic perspective Corsica and Sardinia include members of two separate hormogastrid lineages. The species located in Corsica and Northern Sardinia are related to Vignysa, whereas Hormogaster pretiosa pretiosa, from Southern Sardinia, is closely related to the Hormogaster species from the NE Iberian Peninsula. A molecular dating of the tree using the separation of the Sardinian microplate as a calibration point (at 33 MY) and assuming a model of vicariance indicates that the diversification of Hormogastridae may be ancient, ranging from 97 to 67 Ma.

Latitudinal and altitudinal growth patterns of brown trout Salmo trutta at different spatial scales.

Spatial variation in growth of stream-dwelling brown trout Salmo trutta was explored in 13 populations using a long-term study (1993-2004) in the Bay of Biscay drainage, northern Spain. The high variability in fork length (L(F)) of S. trutta in the study area was similar to the body-size range found in the entire European distribution of the species. Mean L(F) at age varied: 0+ years, 57.4-100.7 mm; 1+ years, 111.6-176.0 mm; 2+ years, 155.6-248.4 mm and 3+ years, 194.3-290.9 mm. Average L(F) at age was higher in main courses and lower reaches compared with small tributaries and upper reaches. Annual specific growth rates (G(L)) were: 0+ to 1+ years, 0.634-0.825 mm mm(-1) year(-1); 1+ to 2+ years, 0.243-0.342 mm mm(-1) year(-1); 2+ to 3+ years, 0.166-0.222 mm mm(-1) year(-1), showing a great homogeneity. Regression models showed that water temperature and altitude were the major determinants of L(F) at age variability within the study area. A broader spatial analysis using available data from stream-dwelling S. trutta populations throughout Europe indicated a negative relationship between latitude and L(F) of individuals and a negative interaction between latitude and altitude. These findings support previous evidence of the pervasive role of water temperature on the L(F) of this species. Altitude appeared as the overall factor that includes the local variation of other variables, such as water temperature or food availability. At a larger scale, latitude was the factor that encompassed these environmental gradients and explained the differences in L(F) of S. trutta. In summary, L(F) at age in stream-dwelling S. trutta decreases with latitude in Europe, the converse of Bergmanns rule.

Spatial Variation in Brown Trout Production: The Role of Environmental Factors

Abstract Spatial variation in Spanish populations of brown trout Salmo trutta was studied in 10 streams of contrasting environmental and biological characteristics based on data compiled over 7 years (1992–1998). Three of the streams had soft water (mean alkalinity as CaCO3 = 19.3 mg/L) supplied by granite catchments at elevations around 1,250 m above sea level and had a low abundance of macroinvertebrates (mean density = 598 individuals/m2; mean biomass = 0.63 g/m2). The remaining streams had hard water (mean alkalinity = 253.6 mg/L) flowing over limestone at 850–1,400-m elevations and possessed a greater benthic faunal abundance (mean density = 2,433 individuals/m2; mean biomass = 2.76 g/m2). Mean brown trout population characters varied significantly throughout the study area (density = 1,567–5,594 fish/ha; biomass = 56.6–240.2 kg/ha; annual production = 47.0–182.0 kg/ha, and the ratio of annual production to mean biomass = 1.01–1.56). A stepwise multiple regression analysis revealed a significant rela...

Appearances can be deceptive: different diversification patterns within a group of Mediterranean earthworms (Oligochaeta, Hormogastridae)

Many recent studies on invertebrates have shown how morphology not always captures the true diversity of taxa, with cryptic speciation often being discussed in this context. Here, we show how diversification patterns can be very different in two clades of closely related earthworms in the genus Hormogaster stressing the risk of using nonspecific substitution rate values across taxa. On the one hand, the Hormogaster elisae species complex, endemic to the central Iberian Peninsula, shows morphological stasis. On the other hand, a clade of Hormogaster from the NE Iberian Peninsula shows an enormous morphological variability, with 15 described morphospecies. The H. elisae complex, however, evolves faster genetically, and this could be explained by the harsher environmental conditions to which it is confined—as detected in this study, that is, sandier and slightly poorer soils with lower pH values than those of the other species in the family. These extreme conditions could be at the same time limiting morphological evolution and thus be responsible for the observed morphological stasis in this clade. Contrarily, Hormogaster species from the NE Iberian Peninsula, although still inhabiting harsher milieu than other earthworm groups, have had the opportunity to evolve into a greater morphological disparity. An attempt to delimit species within this group following the recently proposed general mixed Yule‐coalescent method showed a higher number of entities than expected under the morphospecies concept, most probably due to the low vagility of these animals, which considerably limits gene flow between distant conspecific populations, but also because of the decoupling between morphological and genetic evolution in the H. elisae complex.

Population and family structure of brown trout, Salmo trutta, in a Mediterranean stream

The physical arrangement of closely related individuals is expected to significantly influence the pattern of population genetic structure. For example, if related individuals are non-randomly distributed and included in samples, this may lead to exaggerated conclusions about genetic differentiation. In the present study, we compared population structure v. family relationships of brown trout (Salmo trutta L.) along a Mediterranean stream (Pyrenees) by using eight microsatellite loci. Results showed low levels of genetic (FST) differentiation between collections in a 6.5-km transect along the stream, and a significant correlation between genetic and geographical distance matrices, indicating a weak population structure associated with spatial distribution. Our data also indicated that geographical proximity of related individuals in the youngest (0þ ,1 þ) cohorts probably was associated with limited dispersal of younger brown trout from spawning redds. Family relationships provided evidence, however, for movement of adult trout over distances of a few kilometres that probably contributed to the low observed differentiation. Dispersal of adult Mediterranean trout contrasts with the clustering of related older trout observed for some north European rivers and could be related to the reduced productivity in southern stream basins.