PER Winter 2006 Notes for HH lect 4 (2/14/06) 1 Amphibians: diversity, life history, and declining populations 1. The move to land: lobe-finned fish Compared to “ray-finned fish” (salmon, tuna, etc), “lobe-fins” have: • Reduced skeletal elements in their fore and hind fins, • Greater flexibility at what would become elbows and knees, and • More muscularization of proto-limbs (∴ more power and control). • Most lobe-fins (including us) also have choanae (internal nostrils that open into the oral cavity), which allow breathing through the nose. Tetrapods: • Lost anal and dorsal fins • Fully transformed remaining fins into muscularized limbs. • Dactyly (evolution of digits) • Aquatic → terrestrial habitat Why make the move to land? What problems are caused by a move to land? 2. Some diagnostic characters of “modern amphibians” • Glandular skin that contains both mucous and poison glands (but no epidermal structures) • Three-chambered heart (two atria, one ventricle) • Cutaneous respiration (most species also have lungs, but the three-chambered heart does not provide enough pressure to fully inflate the lungs, so amphibian lungs aren’t that efficient) • Complex inner ear anatomy: the “papilla amphibiorum,” a membrane that allows amphibians to hear acoustic signals of less than 1,000 Hz (very low “bass” sounds). • Highly variable chromosome number, genome size, and ploidy. Where Linneaus got it right and where he got it wrong: 3a. Major groups: caecilians (Gymnophiona): Limbless, burrowing, tropical amphibians • Circumtropical (except Madagascar) • Adults are almost entirely subterranean (and therefore mostly blind) • Internal fertilization, plus some very interesting parental care and reproductive modes. 3b. The salamanders (Caudata): salamanders (and newts, which are just a small group of often aquatic salamanders within the family Salamandridae) • The only major group of amphibians with both tails and limbs • Most diverse in SE U.S.—adaptive radiation spread them to most of North America and some of Central America, plus a few in Europe and east Asia (while ancient landmass of Laurasia existed).PER Winter 2006 Notes for HH lect 4 (2/14/06) 2 Salamander life histories • Most common life history: aquatic larvae, terrestrial adults, internal fertilization via spermataphore, eggs laid in water. (True amphibious lifestyle) • Alternate life histories: paedomorphosis. Reproductive adults retain larval characteristics, typically those associated with an aquatic lifestyle (these individuals live their entire lives in water). Adaptations include retention of external gills and dorsal fins. Species may have obligate or facultative paedomorphosis. • Notophthalmus viridescens (“Eastern Newt”). 3 part life history: Aquatic larvae metamorphose into terrestrial, non-reproductive efts, which stay on land for several years before metamorphosing again into aquatic, reproductive adults. How do salamanders breathe? What are the respiratory organs of salamanders? Body shape can drive ecology & behavior: Being lungless, plethodontids have evolved long, thin bodies, yielding high surface area: volume ratios for increased efficiency of cutaneous respiration. What is the downside of this body shape? 3c. Diagnostic features of Anura: What makes a frog a frog? • The tailless amphibians: postsacral vertebrae are fused into the “tailbone”. • Various adaptations for jumping, including elongated, fused hindlimbs. • Most frogs have no ribs. • More geographically widespread than Gymnophiona or Caudata, but still more prevalent in the tropics than elsewhere. • Most are nocturnal. • Almost all anurans have external fertilization, and almost all are oviparous. • Most anurans mate in a posture called amplexus, in which the male grasps the female in the armpits or at the waist. In some species, amplexus can last for months. • Length of breeding season is often limited by climate, or seasonal availability of breeding sites (such as ephemeral pools). Temporal patterns of reproduction can be roughly divided into two types: explosive breeding and prolonged breeding. What generalities are likely to be true regarding which frogs breed explosively, and which have prolonged breeding seasons? Frog life histories: the common mode, and alternate modes: 4. Amphibian habitat • Given that many amphibians spend part of their lives on land, and part in the water, those species are likely to live close to the border between land & water. • Amphibians with “typical” life histories—aquatic larvae and terrestrial adults—can be broadly separated into two types: those that live in lentic, or slow moving water (such asPER Winter 2006 Notes for HH lect 4 (2/14/06) 3 lakes and ponds), and those that live in lotic, or fast moving water (such as rivers and streams). • What might some of the differences between these 2 broad types be? Riparian zone • Definition: terrestrial zone adjacent to the channel (river, stream) which strongly influences, and is strongly influenced by, the channel. A river and its riparian zone exchange material both on the surface and below the surface (in the hyporheic zone and water table). The riparian zone usually includes the floodplain plus some upslope / terrace land. • In Western WA, torrent salamanders, (Rhyacotriton) giant salamanders (Dicamptodon), & tailed frogs (Ascaphus) live in the riparian zone of semi-seasonal fast-moving streams. Effects of forests on rivers • Shading from solar radiation (temperature and light). A forested riverbank is cooler and darker than an unforested bank. Remove the buffer, ⇑T & rate of evapotranspiration. • Input of nutrients and sediments from upslope and from uptree (leaves, large woody debris). Remove the buffer, ⇑ erosion and siltation. • Riparian (buffer) zones also serve to intercept (excess) N from cropland and pasture. • Habitat creation for aquatic communities along banks (roots, treefalls) Effects of rivers on forests • Streams, and therefore riparian forests, are quite different depending on what stream order they belong to. • Amphibians move frequently between rivers and forests, thus keeping nutrients moving between them as well. • Nutrients in riparian forests come, in part, from streams, some of which ultimately comes from the marine