Fish Reproduction and Development

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Fish Reproduction and Development

• Coevolved traits for producing another generation
  that will produce another generation...and
  another...and another...

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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

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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
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Reproductive traits that vary with life-history
patterns

• Fecundity (no. 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

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Reproductive traits that vary with life-history
patterns

• Size of offspring
• probability of survival increases with 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

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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
• Monogamy - mating pair remains together over
  time, long gestation of young (some cichlids,
  seahorses, pipefish)

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Reproductive frequency

• Single spawning effort in life (semelparous),
• metabolic efficiency
• max. fecundity
• match offspring to ideal growing conditions
• overwhelm predators
• risk of waiting (death)

• Repeated spawning efforts (iteroparous)
• spawn before death
• spread offspring over multiple entry times
• reduce fecundity to ensure SOME reproduction

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To loveem 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)

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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

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Reproductive traits (cont.)

• Method of fertilization
• most fishes use external fertilization
• 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

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Reproductive traits (cont.)

• Method of fertilization, cont.
• 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 fertilizationsperm swallowing?? Yep!
• Callichthyid catfish (Corydoras) Why,
  why...?

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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
• protogynous female first, male later (most
  common, Wrasses)

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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)

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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

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Reproductive traits

• Reproductive morphology, bony fishes
• male testes -gt vas deferens -gt urogenital pore
• female ovary -gt oviduct -gt urogenital pore

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Reproductive traits that vary with life-history
patterns

• Reproductive morphology, cartilaginous fishes
• male testes -gt Leydigs gland -gt seminal vesicle
  -gt cloaca -gt claspers
• female ovary -gt ostium tubae -gt oviduct -gt shell
  gland -gt uterus -gt cloaca

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Female
Male
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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

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Behavioral adaptations for reproduction

• Care-giving behavior - Balons classification
• Non guarders
• Guarders
• Bearers
• See handout! Much diversity here!

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Behavioral adaptations for reproduction

• Care-giving behavior - Balons classification
• Non guarders
• open substrate spawners
• brood hiders
• Guarders
• Bearers

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Behavioral adaptations for reproduction

• Care-giving behavior - Balons classification
• Non guarders
• Guarders
• substratum choosers
• nest spawners
• Bearers

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Behavioral adaptations for reproduction

• Care-giving behavior - Balons classification
• Non guarders
• Guarders
• Bearers
• Guarders
• Bearers
• external
• internal

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FishDevelopment

• Balons theory of
• saltatory development
• Development occurs as a series of discrete
  transitions in form and function (thresholds or
  metamorphoses), with periods of change in size
  (periods) between thresholds

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Developmental stages in fishes

• PERIODS
• EMBRYO
• LARVA
• JUVENILE
• ADULT
• SENESCENT

• THRESHOLDS
• fertilization
• exogenous feeding
• full fin development, body shape of adult
• reproduction
• cessation of growth, fertility

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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...