Genetic diversity and phylogeography of Corynosoma australe Johnston, 1937 (Acanthocephala: Polymorphidae), an endoparasite of otariids from the Americas in the northern and southern hemispheres.

Adult specimens of Corynosoma australe Johnston, 1937 were recorded from the intestines of California sea lions, Zalophus californianus (Lesson), from Baja California Peninsula, Mexico, whereas larval forms were collected from two fish species on the Argentinian coast. Adult specimens of C. australe were morphologically characterized by having a cylindrical proboscis with 18-20 rows of 12-14 hooks per row and a cylindrical trunk expanded anteriorly into a disk with tiny, triangular spines spreading almost to three quarters of the hind-trunk in males and to the posterior body end in females. The aim of this study was to explore the genetic diversity and systematic position of C. australe distributed in the Americas. Newly generated sequences of the mitochondrial cytochrome c oxidase subunit 1 (cox 1) gene were compared with sequences available from GenBank. Phylogenetic analyses performed with the cox 1 dataset using maximum likelihood and Bayesian inference showed that the 11 new sequences of C. australe recovered from the California sea lion in northern Mexico plus the six sequences from Argentinian seashores formed a clade with other sequences of specimens previously identified as C. australe. The intraspecific genetic divergence among the isolates was very low, ranging from 1 to 1.7%, and in combination with the phylogenetic trees confirmed that the isolates belonged to the same species. The cox 1 haplotype network inferred with 27 sequences revealed 18 haplotypes divided into two clusters clearly separated from each other by 5 substitutions. The first cluster corresponded to specimens from the Northern Hemisphere (United States of America and Mexico), and the second corresponded to specimens from the Southern Hemisphere (Argentina and Brazil). The current evidence suggests that C. australe has an amphitemperate distribution and is associated mainly with otariids with secondary and independent colonization events to other mammals and the Magellanic penguin in the Southern Hemisphere.

Review of California sea lion (Zalophus californianus) abundance, and population dynamics in the Gulf of California

Introduction: The life history of the California sea lion (Zalophus californianus) in the Gulf of California is marked by a series of important events influencing and modifying its population growth, distribution, and evolution. Despite the fact that this population has been studied since the 1950s, research has been rather punctual and fragmentary. Before 2010, there are only a few surveys conducted simultaneously in all rookeries, thus there is no reliable information on key aspects of life cycle, population trend and potential threats. In the present work we conducted a review of California sea lion life history and environmental changes in the Gulf of California thorough a collation survey data encompassing the last 37 years. Objective: Our aim was focused on identifying short- and long-term processes potentially acting on the population, and hopefully improve knowledge about the population trend and status using different points of view. Methods: We collected and analyzed population survey data from different sources since the 1970s to 2018: published papers, master's and doctoral thesis, in addition to technical reports. The survey data are organized in sections corresponding with crucial population life history events. Results: Considering a long-time period the population size appears to be stable with zero growth. Cyclic interannual fluctuation seem to denote a certain dependence with climatic factors, not directly with El Niño, but with sea surface temperature anomalies that determine prey availability. However, many doubts persist about the incidence of different local environmental factors on gender and age, particularly related with juvenile recruitment and female survival rate. Conclusions: In conclusion, more information is required based on seasonal surveys, life cycle, regional environmental variation. Statistical errors need to be assessed and monitoring methods should be standardized and must be considered to ascertain short- and long-term population and colony spatial-temporal patterns.

Introducción: El lobo marino de California (Zalophus californianus) en el Golfo de California se caracteriza por una serie de eventos que influyen en el crecimiento, evolución y distribución de la población. Los estudios poblacionales iniciaron en 1950, aunque las investigaciones fueron puntuales y fragmentadas. Antes de 2010 existen pocos censos simultáneos de las 13 colonias de lobos marinos, con los cuales se obtuvo información sobre el ciclo de vida, la tendencia poblacional y las potenciales amenazas de estos organismos. Objetivo: En esta investigación se presenta un resumen de 37 años de historia de investigaciones del lobo marino de California y del ecosistema del Golfo de California. Métodos: Se realizó un análisis de los procesos de corto y largo plazo que actúan sobre la población, revelando aspectos poco conocidos. Se recolectaron y analizaron datos para el periodo de 1970 al 2018: artículos, tesis de posgrado y reportes técnicos, que fueron organizados en secciones relacionadas con eventos ambientales cruciales para la población. Resultados: A largo plazo, la población parece estar estable y presenta fluctuaciones interanuales cíclicas que evidencian dependencia con factores climáticos como anomalías de temperatura superficial del mar regional que determinan un cambio en la disponibilidad de presas para los lobos marinos. No es claro el posible efecto que factores ambientales locales puedan ocasionar en las diferentes clases de edad y por sexos, en particular sobre el reclutamiento de juveniles y la tasa de supervivencia de las hembras. Conclusiones: El presente trabajo identifica las prioridades de información para esta población y ofrece recomendaciones como el monitoreo estandarizado y la consideración de variaciones espacio-temporales locales.