Limits...
Spatial mosaic evolution of snail defensive traits.

Johnson SG, Hulsey CD, de León FJ - BMC Evol. Biol. (2007)

Bottom Line: Recent models suggest that escalating reciprocal selection among antagonistically interacting species is predicted to occur in areas of higher resource productivity.Using spatial autocorrelation to account for genetic and geographic divergence among populations, we found no autocorrelation among populations at small geographic and genetic distances for the two defensive traits.These local geographic differences may result from among-habitat variation in how resource productivity interacts to promote escalation in prey defenses.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148, USA. sgjohnso@uno.edu

ABSTRACT

Background: Recent models suggest that escalating reciprocal selection among antagonistically interacting species is predicted to occur in areas of higher resource productivity. In a putatively coevolved interaction between a freshwater snail (Mexipyrgus churinceanus) and a molluscivorous cichlid (Herichthys minckleyi), we examined three components of this interaction: 1) spatial variation in two putative defensive traits, crushing resistance and shell pigmentation; 2) whether abiotic variables or frequency of molariform cichlids are associated with spatial patterns of crushing resistance and shell pigmentation and 3) whether variation in primary productivity accounted for small-scale variation in these defensive traits.

Results: Using spatial autocorrelation to account for genetic and geographic divergence among populations, we found no autocorrelation among populations at small geographic and genetic distances for the two defensive traits. There was also no correlation between abiotic variables (temperature and conductivity) and snail defensive traits. However, crushing resistance and frequency of pigmented shells were negatively correlated with molariform frequency. Crushing resistance and levels of pigmentation were significantly higher in habitats dominated by aquatic macrophytes, and both traits are phenotypically correlated.

Conclusion: Crushing resistance and pigmentation of M. churinceanus exhibit striking variation at small spatial scales often associated with differences in primary productivity, substrate coloration and the frequency of molariform cichlids. These local geographic differences may result from among-habitat variation in how resource productivity interacts to promote escalation in prey defenses.

Show MeSH

Related in: MedlinePlus

Representative images (A-C) of the hydrobiid snail, Mexipyrgus churinceanus, collected from nearby populations to illustrate small scale variation in size and shell pigmentation. Herichthys minckleyi papilliforms (right figure D) exhibit gill arches modified into more gracile pharyngeal jaws with small muscles and pointed teeth that are ineffective at crushing snails while H. minckleyi molariforms (left figure D) have robust muscles and enlarged crushing teeth on their pharyngeal jaws that seem clearly modified to crush snails. Figure E portrays heterogeneity in habitats with Nymphaea (top) and without Nymphaea (bottom).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC1851949&req=5

Figure 2: Representative images (A-C) of the hydrobiid snail, Mexipyrgus churinceanus, collected from nearby populations to illustrate small scale variation in size and shell pigmentation. Herichthys minckleyi papilliforms (right figure D) exhibit gill arches modified into more gracile pharyngeal jaws with small muscles and pointed teeth that are ineffective at crushing snails while H. minckleyi molariforms (left figure D) have robust muscles and enlarged crushing teeth on their pharyngeal jaws that seem clearly modified to crush snails. Figure E portrays heterogeneity in habitats with Nymphaea (top) and without Nymphaea (bottom).

Mentions: Mexipyrgus churinceanus as well as its polymorphic fish predator Herichthys minckleyi are endemic to the isolated Cuatro Ciénegas valley in the Mexican Chihuahuan desert (Fig. 1) and exhibit putatively co-evolved phenotypes [7-9]. These phenotypes may currently be coevolving because Mexipyrgus exhibits striking examples of morphological differentiation in shell morphology and pigmentation among habitats [[10-12]; Fig. 2]. Herichthys minckleyi is also unusual because this cichlid fish exhibits two alternative pharyngeal jaw morphologies [[13,14]; Fig. 2]. In "papilliform" H. minckleyi, the gill arches are modified into a gracile pharyngeal jaw and this morph is specialized to shred aquatic plants and detritus [15]. Alternatively, "molariforms" possess enlarged crushing molariform teeth and robust pharyngeal muscles [16] and are extremely proficient at crushing M. churinceanus [15]. Molariform cichlids are the primary snail-crushing predator in Cuatro Ciénegas.


Spatial mosaic evolution of snail defensive traits.

Johnson SG, Hulsey CD, de León FJ - BMC Evol. Biol. (2007)

Representative images (A-C) of the hydrobiid snail, Mexipyrgus churinceanus, collected from nearby populations to illustrate small scale variation in size and shell pigmentation. Herichthys minckleyi papilliforms (right figure D) exhibit gill arches modified into more gracile pharyngeal jaws with small muscles and pointed teeth that are ineffective at crushing snails while H. minckleyi molariforms (left figure D) have robust muscles and enlarged crushing teeth on their pharyngeal jaws that seem clearly modified to crush snails. Figure E portrays heterogeneity in habitats with Nymphaea (top) and without Nymphaea (bottom).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1851949&req=5

Figure 2: Representative images (A-C) of the hydrobiid snail, Mexipyrgus churinceanus, collected from nearby populations to illustrate small scale variation in size and shell pigmentation. Herichthys minckleyi papilliforms (right figure D) exhibit gill arches modified into more gracile pharyngeal jaws with small muscles and pointed teeth that are ineffective at crushing snails while H. minckleyi molariforms (left figure D) have robust muscles and enlarged crushing teeth on their pharyngeal jaws that seem clearly modified to crush snails. Figure E portrays heterogeneity in habitats with Nymphaea (top) and without Nymphaea (bottom).
Mentions: Mexipyrgus churinceanus as well as its polymorphic fish predator Herichthys minckleyi are endemic to the isolated Cuatro Ciénegas valley in the Mexican Chihuahuan desert (Fig. 1) and exhibit putatively co-evolved phenotypes [7-9]. These phenotypes may currently be coevolving because Mexipyrgus exhibits striking examples of morphological differentiation in shell morphology and pigmentation among habitats [[10-12]; Fig. 2]. Herichthys minckleyi is also unusual because this cichlid fish exhibits two alternative pharyngeal jaw morphologies [[13,14]; Fig. 2]. In "papilliform" H. minckleyi, the gill arches are modified into a gracile pharyngeal jaw and this morph is specialized to shred aquatic plants and detritus [15]. Alternatively, "molariforms" possess enlarged crushing molariform teeth and robust pharyngeal muscles [16] and are extremely proficient at crushing M. churinceanus [15]. Molariform cichlids are the primary snail-crushing predator in Cuatro Ciénegas.

Bottom Line: Recent models suggest that escalating reciprocal selection among antagonistically interacting species is predicted to occur in areas of higher resource productivity.Using spatial autocorrelation to account for genetic and geographic divergence among populations, we found no autocorrelation among populations at small geographic and genetic distances for the two defensive traits.These local geographic differences may result from among-habitat variation in how resource productivity interacts to promote escalation in prey defenses.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148, USA. sgjohnso@uno.edu

ABSTRACT

Background: Recent models suggest that escalating reciprocal selection among antagonistically interacting species is predicted to occur in areas of higher resource productivity. In a putatively coevolved interaction between a freshwater snail (Mexipyrgus churinceanus) and a molluscivorous cichlid (Herichthys minckleyi), we examined three components of this interaction: 1) spatial variation in two putative defensive traits, crushing resistance and shell pigmentation; 2) whether abiotic variables or frequency of molariform cichlids are associated with spatial patterns of crushing resistance and shell pigmentation and 3) whether variation in primary productivity accounted for small-scale variation in these defensive traits.

Results: Using spatial autocorrelation to account for genetic and geographic divergence among populations, we found no autocorrelation among populations at small geographic and genetic distances for the two defensive traits. There was also no correlation between abiotic variables (temperature and conductivity) and snail defensive traits. However, crushing resistance and frequency of pigmented shells were negatively correlated with molariform frequency. Crushing resistance and levels of pigmentation were significantly higher in habitats dominated by aquatic macrophytes, and both traits are phenotypically correlated.

Conclusion: Crushing resistance and pigmentation of M. churinceanus exhibit striking variation at small spatial scales often associated with differences in primary productivity, substrate coloration and the frequency of molariform cichlids. These local geographic differences may result from among-habitat variation in how resource productivity interacts to promote escalation in prey defenses.

Show MeSH
Related in: MedlinePlus