Roger D. Sepúlveda

Differential ecological responses to environmental stress in the life history phases of the isomorphic red alga Gracilaria chilensis (Rhodophyta)

In order to better understand the alternation of generations that characterizes haploid–diploid life cycles, we assessed the existence of ecological differences between the two phases (haploid gametophyte and diploid tetrasporophyte) in Gracilaria chilensis, a rhodophyte with a typical Polysiphonia-type life cycle. We investigated the effect of light intensity and salinity on viability and growth of both phases at different ontogenetic stages: juveniles and adults. In our study, the survival of juvenile gametophytes (n) was higher than the survival of juvenile tetrasporophytes (2n) despite culture conditions; however, low salinity had greater effect on carpospores (2n) than on tetraspores (n). On the other hand, a complex interaction between salinity and light intensity within each life history phase generated observed differences between juvenile growth rates. Low light was shown to trigger early onset of alteration of the holdfast growing pattern. In addition, adult tetrasporophytes showed, despite the conditions, a faster vegetative growth than female and male gametophytes. These differences between phases could have led to the complete dominance of tetrasporophyte fragments of fronds observed in G. chilensis farms. We hypothesize that Chilean fishers could have unknowingly selected for tetrasporophyte thalli during domestication of the species, thus enhancing the natural trend of tetrasporophytes dominance already present in estuarine natural populations of free-floating plants.

Clinal variation in the shell morphology of intertidal snail Acanthina monodon in the Southeastern Pacific Ocean

Abstract In this study we determine clinal variation of Acanthina monodon shell morphology along the southeastern Pacific coast. Our goals were to describe the clinal variation between biogeographical areas, and between localities along the latitudinal gradient between 30° and 54°S. Specimens were collected from 12 localities throughout the entire geographical distribution range of the species. Geometric morphometric analyses were used to evaluate the morphological variation of A. monodon along the Chilean coast. Relative warps and centroid size scores were used to compare the shape and size and their morphological variation and similarity was evaluated through multivariate analyses between all populations. The first two relative warps explained 78% variance. Size and shape scores decreased southward showing high biogeographical and latitudinal variation, principally due to both the thickness of the lip and the spire length. Multivariate analyses showed two main morphotypes: northern populations with short spires, thick and smooth lips and robust shells; the other with longer spires, thinner ornamented lips and weak shells associated with southern populations. However, three southern populations showed a merging of characteristics from both morphotypes, which could correspond to an intermediate morphotype or a morphological transitional zone. The results suggest the existence of clinal variation along the southeastern Pacific coast showing two morphotypes to north and south of 41°S, with a feature merging zone that probably extends to 45°S, related to biogeographical areas proposed for the Chilean coast. We suggest that the morphotypes reported are the result of site-specific eco-phenotypes responding to local variation.

Morphologic Variation in Aegla Leach (Decapoda: Reptantia: Aeglidae) from Central-Southern Chile: Interspecific Differences, Sexual Dimorphism, and Spatial Segregation

Abstract How do certain characteristics of organisms, such as sex or species, and certain ecological factors, such as interaction with congeneric individuals, influence the variability of body architecture in an environmental setting over a small spatial scale? Using geometric morphometrics we performed a morphological comparison of the dorsal surface of the carapace of a congeneric guild formed by Aegla araucaniensis, A. denticulata denticulata, and A. abtao. Additionally, we evaluated whether the segregation of microhabitat by congeneric interactions generates variations in the shape of the cephalothorax in A. araucaniensis, comparing a population belonging to the congeneric guild with a close population without congeneric interactions. Changes in cephalothoracic shape are regulated primarily by intrinsic factors, such as the differences between species and sex of individuals. In addition, the congeneric interactions do not affect the expression of the carapace shape in either of the populations of A. araucaniensis. The patterns of variation in cephalothoracic architecture are similar to previous reports based on geometric morphometrics, traditional morphology and descriptive morphology. The interspecific variations are caused mainly by the configuration of the spinous processes at the borders of the carapace, while the variation due to sexual dimorphism is due to an expansion of the longitudinal axis in males and the caudal end of the carapace in females. Morphological responses in A. araucaniensis differ from previous comparisons made with other species of Aegla under similar environmental contexts but over distinct spatial scales. We discuss the sexual dimorphism from an adaptive perspective and propose that the architecture of the cephalothorax in aeglids is a trait conserved and regulated significantly throughout the evolutionary history of the group.

Subtidal macrozoobenthos communities from northern Chile during and post El Niño 1997–1998

Despite a large amount of climatic and oceanographic information dealing with the recurring climate phenomenon El Niño (EN) and its well known impact on diversity of marine benthic communities, most published data are rather descriptive and consequently our understanding of the underlying mechanisms and processes that drive community structure during EN are still very scarce. In this study, we address two questions on the effects of EN on macrozoobenthic communities: (1) how does EN affect species diversity of the communities in northern Chile? and (2) is EN a phenomenon that restarts community assembling processes by affecting species interactions in northern Chile? To answer these questions, we compared species diversity and co-occurrence patterns of soft-bottoms macrozoobenthos communities from the continental shelf off northern Chile during (March 1998) and after (September 1998) the strong EN event 1997–1998. The methods used varied from species diversity and species co-occurrence analyses to multivariate ordination methods. Our results indicate that EN positively affects diversity of macrozoobenthos communities in the study area, increasing the species richness and diversity and decreasing the species dominance. EN represents a strong disturbance that affects species interactions that rule the species assembling processes in shallow-water, sea-bottom environments.

PARAMETROS BIOLOGICO-PESQUEROS DE LA JIBIA, DOSIDICUS GIGAS (ORBIGNY, 1835) (CEPHALOPODA: OMMASTREPHIDAE), FRENTE A LA COSTA DE CHILE CENTRAL (29ºS-40ºS) DURANTE 1993-1994

Se presentan los resultados de dos cruceros de pesca de investigacion de la jibia, Dosidicus gigas (Orbigny 1835) realizados entre julio de 1993 y enero de 1994 en la Zona Economica Exclusiva de Chile comprendida entre los 29o S y 40o S. En cada lance se registro el dia, hora, duracion del lance, asi como el volumen de la captura por lance y maquina potera, para efectuar estimaciones de abundancia relativa. A los ejemplares capturados se les determino la longitud dorsal del manto (LDM), peso total, peso eviscerado, peso manto, sexo y se les extrajo el tracto digestivo, para un analisis del contenido estomacal. Las jibias solo fueron capturadas entre los 29o S y los 30o S. En el primer crucero (invierno) se registraron ejemplares grandes (71 a 98 cm LDM) y chicos (< 44 cm LDM) de ambos sexos, mientras que en el segundo crucero (primavera) se capturaron solo jibias de tamano intermedio (26 a 60 cm LDM). Las distribuciones de frecuencias de tamanos determinadas en los cruceros muestran dos cohortes de D. gigas en la zona de pesca. La dieta no vario entre las estaciones y estuvo compuesta principalmente por peces pelagicos y demersales, secundariamente cefalopodos y ocasionalmente crustaceos pelagicos, incluyendo tambien canibalismo. Las relaciones longitud-peso fueron similares en ambos sexos y se corrobora que las jibias registradas en aguas de Chile, alcanzan pesos mayores a la misma longitud que las poblaciones de jibia de Mexico y Peru

A new species of Benthoctopus Grimpe, 1921 (Cephalopoda: Octopodidae) from the southeastern Pacific Ocean

ABSTRACT A new species of the genus Benthoctopus is described and illustrated based on 14 specimens collected from the coast of Central Chile and the Juan Fernández Archipelago, at depths between 436 and 1000 m. This medium sized species (total length between 425 and 770 mm) has no ink sac and presents the following attributes: small biserial suckers; large eyes (diameter between 11 and 23 mm); the first pair of arms longer than the other arms; 63 to 75 suckers in the hectocotylized arm; eight to nine lamellae per demibranch and a W-shaped funnel organ. This new species, which we call Benthoctopus longibrachus, is compared to other species in the genus.

Redescription of Robsonella fontaniana (Cephalopoda: Octopodidae)

The genus Robsonella Adam, 1938 belongs to the family Octopodidae and can only be identified by some characters present in males. In this work the species Robsonella fontaniana is redescribed from morphological and morphometric characters of 33 specimens (21 males and 12 females) collected on the central-south coast of Chile, during the years 2003 and 2004, and of 11 specimens (three males and eight females) obtained from the Zoological Museum of Hamburg. New diagnoses for the genus Robsonella and the species R. fontaniana are provided. Sexual dimorphism in R. fontaniana is evident by adult males having enlarged suckers and a shorter third right arm compared to the females. Some morphological characters such as ligula, radula and terminal organ diverticulum make it possible to distinguish this genus clearly from other genera. The ligula of the hectocotylized arm in Robsonella is characterized by a longitudinal groove, rounded tip, large calamus and seven copulatory lamellae. In addition, the first lateral tooth in the radula is crescent-shaped; this allows the identification of Robsonella regardless of sex.

Positive and negative effects of mesograzers on early-colonizing species in an intertidal rocky-shore community.

Abstract The ecological consequences of human‐driven overexploitation and loss of keystone consumers are still unclear. In intertidal rocky shores over the world, the decrease of keystone macrograzers has resulted in an increase in the dominance of herbivores with smaller body (i.e., “mesograzers”), which could potentially alter community assembly and structure. Here, we experimentally tested whether mesograzers affect the structure of rocky intertidal communities during the period of early colonization after the occurrence of a disturbance. A manipulative field experiment was conducted to exclude mesograzers (i.e., juvenile chitons, small snails, amphipods, and juvenile limpets) from experimental areas in an ecosystem characterized by the overexploitation of keystone macrograzers and predators. The results of multivariate analyses suggest that mesograzers had significant effects on intertidal community structure through negative and positive effects on species abundances. Mesograzers had negative effects on filamentous algae, but positive effects on opportunistic foliose algae and barnacles. Probably, mesograzers indirectly favored the colonization of barnacles and foliose algae by removing preemptive competitors, as previously shown for other meso‐ and macrograzer species. These results strongly support the idea that small herbivores exert a firm controlling effect on the assembly process of natural communities. Therefore, changes in functional roles of top‐down controllers might have significant implications for the structure of intertidal communities.

Nonrandom filtering effect on birds: species and guilds response to urbanization.

Abstract Using bird survey data taken in three cities in Southern Chile, we evaluated the hypothesis that changes in community composition from periurban to urban areas are not random. Furthermore, the consistency of species and guild loss was assessed across cities. A consistent pattern of difference in community and guild structure between urban and periurban habitats was found. In addition, a nonrandom loss of species was found in urban areas compared to periurban areas, and non‐native species dominated urban communities in all cities. The average abundance of omnivores, granivores, and habitat generalists was higher in urban areas, while insectivores and open habitat species were more abundant in periurban areas. These results strongly suggest that urban habitats act as filters offering suitable conditions for only a fraction of the bird species present in a given area, and the lack of suitable conditions may be facilitating local biotic homogenization in the three studied cities. The results of this study not only fill a biogeographical knowledge gap, but the work presented here also aids the general understanding of factors that affect community structure in habitats with varied levels of local and global urbanization.

Evaluating habitat suitability for the establishment of Monochamus spp. through climate-based niche modeling.

Pine sawyer beetle species of the genus Monochamus are vectors of the nematode pest Bursaphelenchus xylophilus. The introduction of these species into new habitats is a constant threat for those regions where the forestry industry depends on conifers, and especially on species of Pinus. To obtain information about the potential risk of establishment of these insects in Chile, we performed climate-based niche modeling using data for five North American and four Eurasian Monochamus species using a Maxent approach. The most important variables that account for current distribution of these species are total annual precipitation and annual and seasonal average temperatures, with some differences between North American and Eurasian species. Projections of potential geographic distribution in Chile show that all species could occupy at least 37% of the area between 30° and 53°S, where industrial plantations of P. radiata are concentrated. Our results indicated that Chile seems more suitable for Eurasian than for North American species.