Showing papers by "Jonathan B. Losos published in 2000"
TL;DR: It is shown that Anolis lizards on Caribbean islands meet several expectations of the evolutionary theory, and the slope of the species–area relationship jumps sharply above the threshold of within-island speciation.
Abstract: Large islands typically have more species than comparable smaller islands. Ecological theories, the most influential being the equilibrium theory of island biogeography, explain the species-area relationship as the outcome of the effect of area on immigration and extinction rates. However, these theories do not apply to taxa on land masses, including continents and large islands, that generate most of their species in situ. In this case, species-area relationships should be driven by higher speciation rates in larger areas, a theory that has never been quantitatively tested. Here we show that Anolis lizards on Caribbean islands meet several expectations of the evolutionary theory. Within-island speciation exceeds immigration as a source of new species on all islands larger than 3,000 km2, whereas speciation is rare on smaller islands. Above this threshold island size, the rate of species proliferation increases with island area, a process that results principally from the positive effects of area on speciation rate. Also as expected, the slope of the species-area relationship jumps sharply above the threshold. Although Anolis lizards have been present on large Caribbean islands for over 30 million years, there are indications that the current number of species still falls below the speciation-extinction equilibrium.
534 citations
TL;DR: Not only is hindlimb length a plastic trait in these lizards, but that this plasticity leads to the production of phenotypes appropriate to particular environments, which potentially could have played an important role in the early stages of the Caribbean anole radiation.
Abstract: Species of Anolis lizards that use broad substrates have long legs, which provide enhanced maximal sprint speed, whereas species that use narrow surfaces have short legs, which permit careful movements. We raised hatchling A. sagrei in terraria provided with only broad or only narrow surfaces. At the end of the experiment, lizards in the broad treatment had relatively longer hindlimbs than lizards in the narrow treatment. These results indicate that not only is hindlimb length a plastic trait in these lizards, but that this plasticity leads to the production of phenotypes appropriate to particular environments. Comparison to hindlimb lengths of other Anolis species indicates that the range of plasticity is limited compared to the diversity shown throughout the anole radiation. Nonetheless, this plasticity potentially could have played an important role in the early stages of the Caribbean anole radiation.
269 citations
TL;DR: The existence of habitat-specific sexual dimorphism suggests that adaptation of Anolis species to their environment is more complex than previously appreciated.
Abstract: Sexual size dimorphism (SSD) is the evolutionary result of selection operating differently on the body sizes of males and females. Anolis lizard species of the Greater Antilles have been classified into ecomorph classes, largely on the basis of their structural habitat (perch height and diameter). We show that the major ecomorph classes differ in degree of SSD. At least two SSD classes are supported: high SSD (trunk-crown, trunk-ground) and low SSD (trunk, crown-giant, grass-bush, twig). Differences cannot be attributed to an allometric increase of SSD with body size or to a phylogenetic effect. A third explanation, that selective pressures on male and/or female body size vary among habitat types, is examined by evaluating expectations from the major relevant kinds of selective pressures. Although no one kind of selective pressure produces expectations consistent with all of the information, competition with respect to structural habitat and sexual selection pressures are more likely possibilities than competition with respect to prey size or optimal feeding pressures. The existence of habitat-specific sexual dimorphism suggests that adaptation of Anolis species to their environment is more complex than previously appreciated.
226 citations
TL;DR: A growing number of studies that have used integrative, multidisciplinary approaches and have demonstrated that ecological character displacement appears to be an important ecological and evolutionary phenomenon are being demonstrated.
Abstract: The study of adaptation—a central issue in biology since before the time of Darwin—is currently enjoying a renaissance. Ridiculed two decades ago as following a panglossian paradigm (1) that promulgated “just so stories” rather than testing hypotheses, evolutionary biology has become a vibrant field in which a wide variety of methods—ranging from molecular developmental biology to manipulative field experiments—are used to rigorously test adaptive hypotheses (2). Nowhere is this more evident than in the study of ecological character displacement; a paper by Adams and Rohlf (3) in a recent issue of PNAS is one of a growing number of studies that have used integrative, multidisciplinary approaches and have demonstrated that ecological character displacement appears to be an important ecological and evolutionary phenomenon.
183 citations
TL;DR: Analysis of the habitat use, locomotion, display, and foraging behavior of C. barbatus and C. porcus shows relatively rapid evolution, rather than antiquity of the lineage, suggesting that the generic name Chamaeleolis might be subsumed within Anolis.
Abstract: Morphologically, the five recognized species of Chamaeleolis (C. agueroi, C. barbatus, C. chamaeleontides, C. guamuhaya, and C. porcus), all endemic to Cuba, are among the most bizarre West Indian lizards. Chamaeleolis is characterized by a prominent bony head casque, relatively large body size (snout-vent length [SVL] of up to 177 mm), proportionately short limbs, cryptic coloration, the ability to move its eyes independently, and lack of tail autotomy (Wilson, 1957; Garrido and Schwartz, 1968; Williams and Rand, 1969). Based on these features, Chamaeleolis traditionally has been considered to be an early offshoot of the anoline lizard radiation that diverged prior to the evolution of Anolis (Etheridge, 1960; Williams, 1969). However, recent molecular systematic studies indicate that Chamaeleolis evolved within Anolis (Hass et al., 1993; Jackman et al., 1999), suggesting that the unusual morphology of Chamaeleolis indicates relatively rapid evolution, rather than antiquity of the lineage (and also suggests that the generic name Chamaeleolis might be subsumed within Anolis [Hass et al., 1993; Jackman et al., 1999]). Few published reports exist on the ecology and behavior of Chamaeleolis. Wilson (1957, 1994) commented on the sluggish behavior of a captive C. porcus named Methuselah, noting that it would remain in the same spot for hours or even days without changing position. Gorman et al. (1969) mentioned that captive C. porcus actively moved between perches, jumped toward prey (crickets, grasshoppers, and mealworms), and displayed to each other by extending their dewlaps, opening their mouths and protruding their tongues. Garrido (1982) suggested that the simple courtship display repertoire in C. barbatus, which consists only of head-bobs displays, supported the idea that Chamaeleolis diverged early in the anole radiation. All previous observations on Chamaeleolis have been conducted on captive animals. During the course of field work on the community ecology of Cuban anoles in 1997 and 1999, we had the opportunity to study the behavior and ecology of this lizard under natural conditions. Here we report data on the habitat use, locomotion, display, and foraging behavior of C. barbatus and C. porcus. Observations on C. barbatus were conducted at So-
21 citations