Evolution, 4th Edition

48 CHAPTER 2

exceptions to Dollo’s law [3]. The ancestral life history pattern of salamanders

includes an aquatic larval stage with features such as gills and parts of the skele-

ton that differ from the adult stage. The aquatic larval stage, characteristic of most

salamanders, has been lost in the evolution of the terrestrial subfamily Plethod-

ontinae, but phylogenetic analysis showed that it has been regained in one lin-

eage of this subfamily, the dusky salamanders (Desmognathus; FIGURE 2.21).

However, the terrestrial plethodontines develop certain features of the aquatic

larval skeleton as they develop in the egg, even though they have adult features

when they hatch [19]. This observation suggests that the genetic and develop-

mental potential for producing a “lost” character may persist for a long time, and

be capable of again generating the lost phenotype under some conditions.

Convergent features are often adaptations by different lineages to similar

environmental conditions. In fact, a correlation between a particular convergent

character in different groups and a feature of those organisms’ environment or

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Ensatina eschscholtzii

Aneides lugubris

A. aeneus

Phaeognathus hubrichti

Desmognathus wrighti

D. quadramaculatus

D. brimleyorum

D. monticola

Plethodon cinereus

Plethodontidae

Other families

(e.g., Salamandridae)

P. serratus

P. ouachitae

P. yonahlossee

P. welleri

P. elongatus

P. vehiculum

P. vandykei

D. aeneus

FIGURE 2.21 A violation of Dollo’s law is illustrated by the larval stage in salamanders.

Red lineages have an aquatic larval stage; green lineages lack this stage and undergo

direct development to the adult form. Most families of salamanders (e.g., Salamandri-

dae) have an aquatic larval stage, an ancestral feature of salamanders. It is absent—a

derived state—in most members of the family Plethodontidae (green lineages). But one

lineage of this family has aquatic larvae, as shown in red: Desmognathus quadramacu-

latus, D. brimleyorum, and D. monticola. Because this lineage is phylogenetically

nested within a large group of taxa that lack the larval stage, we can infer that the

aquatic larval stage has re-evolved. (After [2].)

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