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Fish Reproduction and Development Coevolved traits for producing another generation that will produce another generation...and another...and another... Coevolution of reproduction and development Bioenergetic equation: I=M+G+R+E Surplus energy can be spent on Growth, Reproduction, or some combination of G & R Coevolution of reproduction and development • Linkage between reproductive traits and development patterns • Represent tradeoffs between: – risks & benefits of continued growth vs. reproduction – quantity of offspring vs. quality of offspring – risk of predation vs. chance of finding quality food Octopus larvae Reproductive traits that vary with life-history patterns • Fecundity (number of eggs): – increases geometrically with body size – early growth and deferred reproduction lead to higher fecundity – early growth and deferred reproduction increase probability of dying before reproducing! Reproductive traits that vary with life-history patterns • Size of offspring: – chance of survival increases with increasing size of offspring • larger supply of reserves • fewer potential predators • greater feeding efficiency – cost of producing offspring increases with size – fecundity is reduced as offspring size increases Reproductive traits that vary with life-history patterns • Mating system: – Promiscuous - both sexes with multiple partners - most (common) – Polygynous - males with multiple mates (cichlids) – Polyandry - females with multiple mates – few (Anglerfish, males “parasitize” females, clownfish) – Monogamy - mating pair remains together over time, long gestation of young (some cichlids, seahorses, pipefish) What if this was your lot in life?? Who’s your daddy?? Reproductive frequency • Single spawning effort in • Repeated spawning life (semelparous), efforts (iteroparous) – metabolic efficiency – spawn before death – max. fecundity – spread offspring over – match offspring to ideal multiple entry times growing conditions – reduce fecundity to ensure – overwhelm predators SOME reproduction – risk of waiting (death) “ To love’em and leave ‘em, or not..” • Parental care – increases probability of offspring survival • due to reduced predation risk • due to increased access to food – costs energy - reduces fecundity – takes many forms • brood hiding (behavioral) • nest guarding (behavioral) • internal gestation (physiological) Reproductive traits (cont.) • Parental care, cont. – male care givers - mostly behavioral (advantage?) – female care givers - mostly physiological • oviparous – (egg laying) with behavioral care - yolk fed (lecithotrophy), external development • ovoviviparous – embryo within female, yolk-fed, internal devel. • viviparous – live birth yolk supplemented (matrotrophy), internal development – biparental care Reproductive traits (cont.) • Method of fertilization: – external fertilization (most fish) • less time and energy in courtship, pair bonding • increases number of potential mates • greater fecundity – internal fertilization in few groups: • sharks, rays, skates, ratfishes (Chondrichthyes) • guppies, mollies, etc. - Poeciliidae, Goodeidae • surfperches - Embiotocidae Is internal fertilization better? – internal fertilization requires • lengthy courtship, preparation for mating • intromittent organ – claspers (pelvic fins) in Chondrichthyes – modified anal fin in poeciliids, goodeids – modified genital papilla in embiotocids • male structure for storing sperm (seminal vesicle) – buccal fertilization—sperm swallowing?? Yep! Callichthyids (“Corydoras”) Why, why, why? Reproductive traits that vary with life-history patterns • Gender system: – most are gonochoristic (single sex, fixed at maturity) – some are hermaphroditic • simultaneous hermaphrodites function as male and female at same time (23 families; ex. Anguilliformes, eels; Atheriniformes, killifish) • sequential hermaphrodites start life as one sex, change sex after maturity – protandrous: male first, female later (clownfish) – protogynous: female first, male later (most common, Wrasses) Reproductive traits that vary with life-history patterns • Gender system (cont.): – Parthenogenetic: • gynogenetic – sperm needed for egg development, but mating without fertilization (triploid - triploid eggs), result is daughters are genetic clones of mothers (Amazon molly, Poecilia formosa) • hybridogenetic - egg development with fertilization by males of other species, but male genes discarded at next generation (diploid - haploid eggs) Reproductive traits that vary with life-history patterns • Secondary sexual characteristics – monomorphic (males and females alike) – permanently dimorphic (mature sexes distinguishable) – seasonally dimorphic (mature sexes distinguishable only at spawning time) – polymorphic Reproductive traits • Reproductive morphology, bony fishes: – male: testes -> vas deferens -> urogenital pore – female: ovary -> oviduct -> urogenital pore Reproductive traits that vary with life-history patterns • Reproductive morphology, cartilaginous fishes: – male: testes -> Leydig’s gland -> seminal vesicle -> cloaca -> claspers – female: ovary -> ostium tubae -> oviduct -> shell gland -> [uterus] -> cloaca Male Female Behavioral adaptations for reproduction • Courtship - color, size, movements important • Spawning site selection – substrate spawners - broadcast – water-column spawners - broadcast – site preparers – internal fertilization - also may be habitat- specific Behavioral adaptations for reproduction • Care-giving behavior - Balon’s classification: – Non guarders – Guarders – Bearers Behavioral adaptations for reproduction • Care-giving behavior - Balon’s classification: – Non guarders • open substrate spawners • brood hiders – Guarders – Bearers Behavioral adaptations for reproduction • Care-giving behavior - Balon’s classification: – Non guarders – Guarders • substratum choosers • nest spawners – Bearers Behavioral adaptations for reproduction • Care-giving behavior - Balon’s classification: – Non guarders – Guarders – Bearers • Guarders • Bearers – external – internal Fish Development • Balon’s theory of saltatory development: – Development in discrete transitions in form and function (thresholds or metamorphoses), with periods of change in size (periods) between thresholds Developmental stages in fishes PERIODS THRESHOLDS EMBRYO fertilization exogenous feeding LARVA full fin development, JUVENILE body shape of adult reproduction ADULT cessation of growth, SENESCENT fertility Developmental stages in fishes • Advantages of saltatory (unique stages) development? – separation of life stages – niche specificity adapted to size • food acquisition • predator avoidance • temperature optimization • others...
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