Transcript Fish Reproduction and Development Coevolved traits for producing another generation that will produce another generation...and another...and another...

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
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
“ 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 habitatspecific
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
EMBRYO
LARVA
JUVENILE
ADULT
SENESCENT
THRESHOLDS
fertilization
exogenous feeding
full fin development,
body shape of adult
reproduction
cessation of growth,
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...