Adaptation or Exaptation An experimental test of hypotheses

Adaptation or Exaptation? An experimental test of hypotheses on the origin of salinity tolerance in Bufo calamita Ivan Gomez-mestre and Miguel Tejedo 2005

• • • Introduction Materials and methods Results Discussion Conclution

• Introduction • • Materials and methods Results Discussion Conclution

Adaptation ØDifferences in phenotype among populations if have a genetic basis. ØConfer fitness advantage in environment. (Endler 1986; Sinervo and Basolo 1996).

Exaptation As a trait evolved for other usages, and later co-opted for its current function. Ø feather Gould & Vrba(1982)

Trait Ø Some traits may share a developmental history in spite of metamorphosis Ø Postmetamorphic traits may be affected by the environment experienced during premetamorphic stages (Goater, 1994; Tejedo et al. , 2000; Relyea, 2001; Relyea & Hoverman, 2003)

• A trait under certain environmental in one life stage could be affected by selection acting on an associated trait from another life stage experiencing a different environment. (Deban & Marks, 2002)

Local adaptation of salinity tolerance • linked to fitness • genetic basis underlying the trait (Gomez-Mestre & Tejedo 2003)

Adaptation or Exaptation? Salinity tolerance may have – direct action of selection – a correlated response to selection acting on some other trait

• Spain populations (even freshwater populations)have shown higher embryonic salinity tolerance than any of the UK populations • steep South-to-North decreasing gradient in genetic diversity (Beebee, 1985)

North-to-South in western Europe • decreasing rainfall • increasing evapotranspiration • increasing summer drought

• freshwater is the standard larval environment • drought is a more common selective pressure than salinity

Exaptation salinity tolerance during embryonic and larval phases drought tolerance during the terrestrial phases • The salinity tolerance traits could have evolved as an exaptation. (Arnold, 1994)

Hypothesis • relies on association between – salinity tolerance in the aquatic stages, – drought tolerance of the terrestrial juvenile and adult stages.

• Introduction • Materials and methods • Results • Discussion • Conclution

Bufo calamita http: //www. herpetofauna. at/amphibien/bufo_calamita. php

Three populations • freshwater environments – Donana – Pedroso • brackish environments – Jarales

• Exposed juveniles to either humid or dry conditions for 5 weeks – survival – growth – behaviour：burying and prey capture

Two hydric potentials • Humid (12 replicates per population) -150 k. Pa • Dry (15 replicates per population) -1150 k. Pa.

vermiculite

Burying and prey capture

• Introduction • Materials and methods • Results • Discussion • Conclution

Survival • Weight at metamorphosis significantly affected survival • Neither population of origin nor humidity significantly affected survival

Growth • Growth was not the same across treatments. • The dry environment significantly reduced growth rate.

• However, neither population of origin nor its interaction with humidity affected growth rate.

Burying • Humidity had a very significant effect on proportion of time spent buried. • Toadlets under dry conditions spent more time buried.

Morphological changes • Body length relative to body mass did not vary significantly between humidity treatments • Population of origin did not affect relative changes in morphology.

Prey capture success Toadlets from the humid treatment – more attempts at prey capture – higher efficiency

• Introduction • Materials and methods • Results • Discussion • Conclution

Decreased growth rates • physiological adjustments, • shifts in behaviour • osmotic stress interfere with the control of tongue

Decreased growth rates • smaller size • reduced ability to capture prey

Lack of association between drought and salinity tolerance • the reaction of the three populations across environments were remarkably paralle • high similarity in drought tolerance among populations

Explain why • First – the level of drought used in the experiment may not have been stressful enough – may be expressed only at the hardest conditions

• Secondly – populations are not isolated – substantial variation in salinity tolerance within freshwater populations

(Gomez-Mestre & Tejedo, 2003)

• Third – different pathways for osmoregulatory physiology may simply – however, dismiss the coupling hypothesis • the information available on tadpole osmoregulation is scarce

• aquatic and terrestrial stages may have different physiological responses to osmotic stress • each evolving independently of the other.

• • Introduction Materials and methods Results Discussion • Conclution

Conclution • Salinity tolerance in the aquatic phase of B. calamita is more likely to have evolved in these populations as an adaptation, rather than an exaptation from drought tolerance.

• Thanks for your attention

• Environmental heterogeneity tends to increase the phenotypic plasticity of traits (when populations exchange migrants) (Rawson and Hilbish 1991; Sultan and Spencer 2002) • However, when migration is restricted, selection under extreme conditions tends to favor local adaptation over plasticity (Pigliucci 2001)

common garden experiments