Histological characteristics of gills and dorsal skin in ambystoma leorae and ambystoma rivulare: morphological changes for living at high altitude / Características histológicas de la piel del dorso y las branquias en ambystoma leorae y ambystoma rivulare: cambios morfológicos para vivir a gran altitud

SUMMARY: Vertebrates exhibit structural changes in their cardiovascular and gas exchange systems in response to hypoxic conditions in high altitude environments. In highland neotenic mole salamanders, as other amphibians, the majority of gases exchange is carried out for skin and gills. But, in high altitude environments, the available oxygen is lower than it is in the air thus, the scarcity of oxygen limits the survival of organisms. Many studies on this subject have focused on understanding the hematological mechanisms that amphibians exhibit in response to hypoxia. However, little is known about possible morphological changes in respiratory structures that may permit increased gas exchange during respiration in high altitude amphibians like Ambystoma leorae and A. rivulare, two threatened Mexican salamander species. The aim of the present study was to describe and compare the histological characteristics of the gills and dorsal skin of A. leorae and A. rivulare from populations at low and high altitudes. We found that, in comparison to lowland organisms, highland ones exhibited more pronounced skin folds, greater numbers of secondary branches in the gills, thinner dorsal and gill epidermises, and greater quantity of melanin surrounding the gill blood vessels. These differences permit a greater capacity for gas exchange and also increase thermoregulatory capacity in high altitude environments.

RESUMEN: Los anfibios que viven en ambientes de altitud se enfrentan a factores abióticos que limitan la vida, tales como la disminución de la presión barométrica con la consecuente disminución de la presión parcial de oxígeno (O2). Conocer los mecanismos que optimizan la obtención del O2 en estos animales es de gran importancia para entender las diferencias en la sensibilidad a la hipoxia de las diferentes especies. Ambystoma rivulare y A. leorae son anfibios endémicos del Estado de México que viven en ambientes de alta altitud por lo que se cree presentan estrategias fenotípicas para asimilar eficazmente el O2 y poder subsistir en los ambientes de altitud. El objetivo de este trabajo fue analizar las características histológicas de branquias y piel cefálica (que son las principales estructuras que se encargan del intercambio gaseoso) provenientes de tres poblaciones con diferente altitud. Nuestros resultados muestran que los organismos que habitan a mayor altitud tienden a aumentar la superficie de intercambio gaseoso, como es el caso de pliegues epidérmicos y ramas branquiales secundarias. Las diferencias histológicas de branquias y piel cefálica tanto interespecíficas como intraespecíficas respecto a la altitud parecen apoyar la idea de que los organismos modifican sus estructuras para contrarrestar las limitantes de la vida en ambientes de altitud.

Infracomunidades de helmintos parásitos de Ambystoma lermaensis (Caudata: Ambystomatidae) en Lerma, México / Infracommunity of parasite helminths of Ambystoma lernaensis (Caudata: Ambystomatidae) in Lerma, Mexico

The helminth infracommunity structure was analyzed in 48 salamanders (Ambystoma lermaensis) from San Pedro Tlaltizapßn, Lerma, Estado de Mexico (June 1997 to March 1999). Richness (2.46 +/- 1.8), abundance (29.5 +/- 42.3), and diversity (0.64 +/- 0.58) levels characterize these communities as depauperate, similar to other amphibian helminth communities worldwide. Apparently, the main forces determining infracommunity structure are ectothermy (as regulator of the ingestion rate), and the opportunistic feeding habits of the hosts, because 80 of the helminth taxa enter the host by ingestion of intermediate hosts.

Histologia de Ixodidae: I. Ovário e traquéia de Amblymma tigrinum (Acari) / Histology of Ixodidae: I. Ovary and trachea of Amblyomma tigrinum (Acari)

I was studied the histology of Amblyomma tigrinum (Ixodidae) an ixodid fick. Three A. tigrinum engorged females were dissected, collected ovary and tracheae, and fixed in Bouin's aqueous fixative during 24 hours; the organs were cut at a thickness of 6-7 um and stained by hematoxylin-eosin. Ovary of A. tigrinum (Fig. 1) showed two cellular layers, similar to the ovary of D. andersoni and B. microplus, being one outer (oocyts) and the inner layer (epithelial cells). Trachea (Fig. 2) showed a cellular layer and a chitions spiral, similar to D. andersoni

Neuroepithelial organs of the lateral line system in urodele amphibians [Ampystoma, Axolotl]

10 full-term larvae and adult urodeles [Ambystoma, axolotl] were used in this study. Serial Epon sections were prepared and stained with toluidine blue. The lateral line receptors in the larval and adult animals consisted of 2 types of organs, the ordinary neuromasts and the ampullary organs. The organs were arranged in different lines in the head and along the whole side of the body. The ampullary organs were restricted only to the head. The 2 types of organs were histologically different in their constituent cells, especially th sensory cells. In the neuromast, the sensory cell showed a single hair, while in the ampullary organ it showed a single striated protrusion. The significances of the distribution, morphology and histological structure of these sense organs were discussed