Vanishing of Characodon
Michael Tobler started his speech with the question: Whence the diversity? He explained several mechanisms of diversification and exponded phenotypic diversification and reproductive isolation in the case of Poecilia mexicana from caves, namely the Cueva del Azufre: H2S and darkness lead to adaptation and speciation: Morphological compared, fish have smaller eyes the deeper they can be foundin the caves, and have bigger heads with extended lateral pores, when there is more sulfur in the water. Then he showed a situation in the genus Cyprinodon, where hybrids eclipse the parental phenotypic variation and are not somehow in the middle between them.
Characodon represents a basal lineage within the Goodeidae. Derived characters are:
• Simple trophotaenia without lateral branches
• Particular ovarian morphology
• More dorsal fin rays in males than females
• Four branchiostegal rays
• 24 chromosomes
• Inhabits springs and their outflow
• Habitats usually with dense macrophytes
• Little known about feeding habits
• Often coexists with Cyprinodon meeki, Gila conspersa, Dionda episcopa, and Menidia mezquital
The separation from last common ancestor with other Goodeinae may have been about 10.5 million years ago (Dominguez et al., 2006). The split caused by the uplift of southeastern part of Sierra Madre Occidental (Dominguez et al., 2006). Tobler introduced the three described species of the genus Characodon:
C. garmani (Parras Characodon)
• Jordan & Evermann, 1898
• Parras drainage
• Only known from a single female specimen
• Spring habitats are destroyed
C. lateralis (Rainbow Characodon)
• Gunther, 1866
• Upper Rio Mezquital drainage
• Relatively widespread
• Convex dorsal profile; males not mostly black & lacking silvery scales; median fins with yellow or red band and a black margin
C. audax (Bold Characodon)
• Smith & Miller, 1986
• Upper Rio Mezquital drainage
• Endemic to El Toboso
• Dorsal profile indented at nape; breeding males dark, sides flecked with silvery scales; no yellow or orange in median fins
Michael Tobler asked four questions and discussed them afterwards:
• What was the historic morphological variation across populations?
• How does morphology relate to geography and phylogenetic relationships?
• What are the implications for taxonomy and conservation?
• What is the current conservation status?
He showed in graphics, that the body shape changes with size and sex and that populations are significantly different in body shape. They are significantly different from each other in morphology and male nuptial colorations. The results show that hydrographic units explain deep splits in morphological differentiation, and that the distinct El Toboso population is consistent with the description of C. audax.
The Morphology suggests splits according to hydrographic units
• Separation of El Toboso (C. audax s. s.)
• Separation between populations below and above the El Salto waterfall
Molecular phylogenetic data are showing not the same situation: They are inconsistent with phylogeny. Though they strengthen the separation in below and above the falls, they do not reveal a separation of the population of El Toboso. So what species do we have and what will have to be done to give us an image of the species?
What is C. audax?
• Based on genetic analyses, all populations above the falls should be named C. audax
• This procedure has implicitly been adopted
• Required re-analysis and re-description of the species
What is C. lateralis?
• Type locality is unknown
• Implicitly type locality is assumed to be Los Berros
• Requires designation of a neotype
• Detailed study of relationship and taxonomic traits is needed!
The current statuses of known populations of Characodon:
Current status of Los Pinos
• Absent in 2011
• 300 m of suitable habitat
• Last record in 2001 by JMAA
Current status of Laguna Seca (Guadalupe Aguilera)
• Present in 2011
• Population apparently stable
• Invasive Oreochromis aureus present
Current status of Cerro Gordo
• Absent in 2011
• Spring has been try potentially for almost 20 years
• Last record in 1982 by RRM
Current status of San Vincente de Chupaderos•
• Absent in 2011
• No specimens found on repeated visits since 1999
• Invasive Goodea atripinnis and Lepomis macrochirus present
• Last record in early 1990s by CS
Current status of Presa PeÒon del Aguila
• Absent in 2011
• No specimens found on repeated visits since 1993
• Invasive Lepomis macrochirus and Micropterus salmoides present
Current status of El Toboso (C. audax)
• Absent in 2011
• Invasive Gambusia senilis present
• Last record in 2006 by JMAA
Current status of El Tobosito
• Absent in 2011
• No specimens found on repeated visits since 2003
• Invasive Gambusia senilis present
• Last record in early 1990s by DI
Current status of Ojo Garabato (27 de Noviembre)
• Present in 2011
• Population apparently stable
• Invasive Oreochromis aureus, Lepomis machrochirus, and Gambusia senilis present
Current status of Los Berros (Ojo de Agua San Juan)
• Present in 2011
• Reduced abundance compared to the past
• Invasive Oreochromis aureus and Xiphophorus hellerii present
Current status of La Constancia
• Present in 2011
• Apparently stable despite small habitat
• Invasive Oreochromis aureus and Xiphophorus hellerii present
Current status of Amado Nervo
• Present in 2011
• Only a single juvenile individual found; numbers appeared stable 1993-2010
• Invasive Oreochromis aureus and Xiphophorus hellerii present
Summary: Characodon is rapidly disappearing:
• Only 4 of formerly 18 populations remain apparently stable
• El Toboso and Amado Nervo recently in critical condition
• 80% reduction in range (other recent estimates ranged from 30-60%; Dominguez-Dominguez et al. 2006, Conserv. Biol.)
The Conservation threats are:
Invasive species
• Predation
• Competition
• Ecosystem effects
Water use
• Surface water diversion
• Ground water use
• Disappearance of habitats
Futhermore: Pollution, Land use changes and Degradation of habitats
Conservation strategies are (following the Desert Fish Council)
• Population monitoring
• Protection and improvement of habitats
• Invasive species removal
• Establishment of refuge populations in artificial and unoccupied habitats
Conservation implications
• Characodon populations need to be managed independently
• Keep stocks separate
Michi Tobler
Oklahoma State University
http://www.sulfide-life.info/mtobler