Biology and Evolution of the Mexican Cavefish

Alex Keene, Masato Yoshizawa, Suzanne Elaine McGaugh

• Publisher: Academic Press
• Year: 2015
• ISBN:
  9780128023655
• Topic: Biological Sciences
• Subtopic: Marine Biology
• Index: Biological Sciences

Biology and Evolution of the Mexican Cavefish features contributions by leading researchers in a comprehensive, unique work that examines a number of distinct areas of biology—evolution, development, ecology, and behavior—using the Mexican cavefish as a powerful model system to further understanding of basic biological processes such as eye degeneration, hearing, craniofacial development, sleep, and metabolic function.

These fish are currently being used to better understand a number of issues related to human health, including age-related blindness, sleep, obesity, mood-related disorders, and aging. The recent sequencing of the cavefish genome broadens the interest of this system to groups working with diverse biological systems, and has helped researchers identify genes that regulate sleep, eye degeneration, and metabolic function.

Mexican cavefish are particularly powerful for the study of biological processes because these fish evolved independently in twenty-nine caves in the Sierra de el Abra Region of Northeast Mexico. These fish have dramatic adaptations to the cave environment, and this can be used to identify genes involved in disease-related traits.

This scholarly text will be of interest to researchers and students throughout diverse areas of biology and ecology. It includes photographs of animals and behavior in laboratory and natural settings that will also increase interest and accessibility to non-experts.

• Includes a mixture of images and illustrations such as the geographical distribution of cave pools and the developmental biology of the nervous system
• Features a companion site with geographical maps
• Fills a notable gap in the literature on a topic of broad interest to the scientific community
• Presents the recent sequencing of the cavefish genome as a groundbreaking development for researchers working with diverse biological systems

Part I

Ecology and Evolution

Chapter 1

Cave Exploration and Mapping in the Sierra de El Abra Region

William R. Elliott Association for Mexican Cave Studies, Missouri Department of Conservation (retired), Jefferson City, Missouri, USA

Abstract

Knowledge about the Mexican cavefish, Astyanax mexicanus, was advanced by biologists, geologists, and cavers over three periods of work: 1936-1954, 1963-1998, and 2009 to present. Hundreds of caves in the Sierra de El Abra region were discovered on the ground or from the air, and explored by Mexican, American, Canadian, and European teams, many participating in the Association for Mexican Cave Studies (AMCS). Twenty-eight of 29 cavefish sites have been mapped. Caving and cave diving techniques advanced over the years, along with cave mapping and cartography. Now the maps and GIS are helping our understanding of the hydrogeological nature of the caves and where they may drain to, thus informing geneticists and their work. Some of the cavefish populations have not been sampled genetically. In the future, dye tracing studies could reveal groundwater flow paths to the region’s springs (nacimientos), which may have very long-distance connections to the caves.

Keywords

Astyanax

cave exploration

cave mapping

cavefish

GIS

karst

Mexico

Sierra de El Abra

Sierra de Guatemala

Acknowledgments

I am grateful to Sharon Mitchell, Linda Mitchell, David Bunnell, and the late professors, Robert W. Mitchell and Francis Abernethy for photographs. Thanks to Gayle Unruh, Gerald Atkinson, and Luis Espinasa for reviewing the manuscript, and to David McKenzie, who for many years has supported cavers with excellent programs such as Walls and WallsMap for cave cartography. Logan McNatt and Bill Mixon helped me many times in gathering up and scanning old survey notes and maps. Thanks to the AIM and the Association for Mexican Cave Studies for their support and for encouraging me to write these chapters.

Introduction

Here I explore the worlds of biology and caving, and summarize what is known about the Mexican cavefish and its habitat. I will discuss the history of discovery, exploration, and mapping of caves in the Sierra de El Abra region (Figures 1.1 and 1.2). Much of this fieldwork was driven by an interest in the cavefish by about 200 biologists, geologists, and cavers (speleologists), who often worked together. Biologists and geologists made the first cavefish discoveries in the region. Only a few of the fish caves can be accessed on foot—vertical caving techniques and training are required in most. Many of the pit caves proved to be too challenging for academics. The cavers were younger explorers and adventurers, some of them graduate students excited by large, deep caves. Some of the professors became proficient in vertical caving, and some of the cavers became cave biologists. Americans, Canadians, Europeans, and Mexicans sometimes worked together in the field and laboratory. It also was a cultural phenomenon; the northerners learned more Spanish, fell in love with Mexico, and worked to create international goodwill. The teams found over 200 caves in the El Abra region, but just 29 of them are known to contain the Mexican cavefish.

Figure 1.1 Asytanax mexicanus, the Mexican cavefish from Cueva de El Pachón. By Jean Louis Lacaille.

Figure 1.2 Aerial photo looking south along the crest of the Sierra de El Abra. By Robert W. Mitchell.

Mexico is home to at least seven known species of cavefishes. These cavefishes have reduced or nearly absent eyes and pigment, and they have evolved from six families from widely separated areas: Characidae, Ictaluridae, Pimelodidae, Poeciliidae, Bythitidae, and Synbranchidae (Reddell, 1981). In this book, we refer to cavefishes of the species Astyanax mexicanus, which include the obsolete genus, Anoptichthys, as the “Mexican cavefish” (Figure 1.1). Whatever the Latin name may be, the Mexican cavefish is an evolving new species that is separating from its river form. The cave form can be purchased in aquarium shops and is easy to keep and breed. The aquarium breed came from La Cueva Chica, described below; it is a hybrid between the river and cave forms (see the chapter on ecology and biodiversity).

A large technical literature exists in biology and speleology (caving) about caves and cavefishes in the Sierra de El Abra region of northeastern Mexico, also referred to as the “Huastecan Province.” (The Huastecs are a group of native Americans in that area, whose language is related to Mayan.) Over 530 papers and reports have been published on the Mexican cavefish since 1936. A monograph on the cavefish was published by Mitchell et al. (1977). Another important study was John Fish’s dissertation (1977, 2004) on karst (limestone cave) hydrology of the region. These monographs are available from the Association for Mexican Cave Studies (AMCS), Austin, Texas at http://www.mexicancaves.org, where thousands of cave maps from throughout Mexico are also available.

I can only present a few maps here and in the next chapter. For additional information and many maps, see The Astyanax Caves of Mexico (Elliott, in press).

Figures 1.3 and 1.4 depict the northern and southern parts of the Sierra de El Abra region, about 200 km long and 60 km wide. See Table 1.1 for a listing of the 29 known fish caves, and Table 1.2 for a list of the larger nacimientos (large springs or resurgences). Another focus of cavefish evolution is in the state of Guerrero, about 400 km to the south of the El Abra, with two populations of Astyanax aeneus (Espinasa et al., 2001).

Figure 1.3 The Sierra de El Abra Region, northern map. Numbers for fish caves and nacimientos (springs) are in Tables 1.1 and 1.2. North is up, white dots are fish caves, triangles are other caves, and squares are nacimientos. By William R. Elliott based on INEGI 1:1,000,000 topographic map (San Luís Potosí sheet) and AMCS data. Copyright © 2016 William R. Elliott. All rights reserved.

Figure 1.4 The Sierra de El Abra Region, southern map. See Tables 1.1 and 1.2. By William R. Elliott. Copyright © 2016 William R. Elliott. All rights reserved.

Table 1.1

The 29 Known Astyanax Caves of the Sierra de El Abra Region, with Label Numbers from Figures 1.3 and 1.4 and Dimensions in Meters

...

Label	Cave	Length	Elevation	Depth	Bottom
1	Sótano (Resumidero) de Jineo	302	292	144	148
2	Sótano del Molino	658	269	138	131
3	Sótano Escondido	100	303	150	153
4	Bee Cave	245	249	119	130
5	Sótano del Caballo Moro	285	320	211	110
6	Sótano de Vásquez	1500	422	277	145
7	Cueva de El Pachón	1000	211	8	203
8	Sótano de Venadito	4419	312	206	106
9	Sótano de Yerbaniz	2027	242	97	145

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Introduction: The Emergence of the Mexican Cavefish as an Important Model System for Understanding Phenotypic Evolution
• Part I: Ecology and Evolution
• Part II: Genetic Diversity and Quantitative Genetics
• Part III: Morphology and Development
• Part IV: Behavior
• Part V: Future Applications
• Concluding Remarks: The Astyanax Community
• Index
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