Ichthyology
Spring 1999
T. Turner

Lecture 5- Reproduction

Fitness; Semel-; iteroparity; Allocation; Mating System; Alternative Life Histories; Gender System; Parental Care

I. Energetics of Reproduction - Reproductive strategies allocation of energy to transmit genes to offspring - patterns of allocation vary

A. Reproductive Effort - energy or time invested in reproduction

1. Assumed to be greater in females - choosy

--number of eggs (fecundity)

--fecundity scales geometrically with length

--size of eggs (reproductive investment per individual)

--trade-off between number and size of eggs

2. Male gametes assumed to be relatively inexpensive, reproductive effort is expended in :

a. courtship

b. territoriality

c. predation - more conspicuous

d. parental care

B. Frequency of Reproduction over lifetime--

1. Semelparous - spawn once in lifetime, putting eggs in one basket

Diadromous-catadromous species do this a lot

2. Iteroparous - spawn more than once over lifetime - even out variance in reproductive success but contribute large amounts of energy to reproduction over lifetime

a. single, extended spawning season (fractional spawning)

b. multiple spawning seasons - long lived fishes

II. Mating Systems

A. Promiscuous - males and females spawn with multiple partners

Examples: Gasterosteidae, Clupiedae, Poeciliidae, Serranidae (Groupers)

Pomatocentridae

B. Polygamous

1. Polygyny (male has multiple partners each breeding season); Examples: Percidae, Centrarchidae, Serranidae, Cottidae, Cichlidae; Pomatocentridae

2. Polyandry (female has multiple partners) Pomacentridae (anemonefishes)

C. Monogamy

(mating partners remain together for extended period, or reform pairs to spawn repeatedly). Examples: Pomatocentridae, Ictaluridae, Chaedontidae, Cichlidae, Blenniidae, Opistognathidae (jawfishes)

III. Gender System

A. Gonochoristic - sex fixed at maturation: most fish species

B. Hemaphroditic - presence of male/female gametes; or sex may change after maturation

1. Simultaneous - both sexes in one individual

Examples: Rivulus, Serranidae (hamlets)

2. Sequential (one sex at maturity and changes to other sex)

a) Protandrous: rare (male first, change to female): Pomatocentridae, some Muraenidae (moray eels)

b) Protogynous; more common (female first, change to male): Gobiidae, Labridae, Scaridae (parrotfishes), Anthias (Serranidae)

C. Parthenogenetic - egg development occurs without fertilization

(Overhead)

1. Gynogenetic - sperm activates egg, makes no genetic contribution

Examples: Poeciliopsis, Poecilia formosa

2. Hybridogenetic - male contribution discarded each generation

Example: Poeciliopsis

IV. Primary sexual characteristics - features involved with copulation or parental care

Gonopodium - Poeciliidae; Claspers (modified pelvic fins) Elasmobranchs, brood patches, pouches, ovipositors

V. Secondary sexual characteristics - four general attributes

A. Four features of secondary sexual characteristics

1. Exclusive or differential expression in one sex - sexual dimorphism

2. Do not appear until maturation

3. Often develop during the breeding season, then regress

4. Do not enhance survival (one component of fitness)

B. Dimorphic Forms-

1. Body size differences, fin shape and size differences

2. Color differences

3. Swelling and/or growth of particular features, kype

4. Body ornamentation: egg mimics, breeding tubercles

5. Electric, Acoustic signal differences (Oyster Toadfish [Batrachoididae-gas bladder muscle)

VI. Spawning Behaviors

A. Non-guarders

1. Open substrate spawners (Broadcasters) - release gametes into water column

a. yields widely dispersed larvae

b. eggs and embryonic forms usually buoyant

c. high mortality, high fecundity

d. often congregate in mass spawning groups

2. Benthic Spawners

a. eggs demersal, can be adhesive

3. Brood hiders

a. Benthic - scoop out depression to bury eggs

- larvae may hide in interstices of gravel until development

b. Crevice spawners - lay eggs in crevice of wood or rock

c. On/In Invertebrates - female bitterlings (Cyprinidae) have long ovipositor, males shed gametes over siphon

d. Annual fishes - lay eggs in mud to survive dry season (some killifishes)

B. Guarders - protect embryos after hatching, 90 out of 420 families of bony fishes; male alone or male plus female --80% of fishes that have parental care --paternity assurance

1. Substrate choosers

a. male cleans substrate before enticing female; 1) rock/plant tenders - gobies; 2) terrestrial - spraying characin; 3) pelagic-floating eggs

2. Nest spawners

a. construct cavity or pit where eggs are laid, enseminated and embryos defended

1. pit nests in gravel or rock, may supplement with grass if muddy

2. kidney secretions to "glue" plant material together, followed by complex courtship

b. froth nests - Siamese fighting fish (Belontiidae)

1. eggs and embryos buoyant, construct bubble nest with secretions to hold bubbles in place

c. cavity nesters - rocks, logs, etc. Percidae, Ictalurid catfishes

d. anemone nesters--clownfishes

C. Bearers-- carry embryos internally or externally

1. External

a. transfer brooders. Medaka (Cyprinidontidae) eggs attached to female's belly until transferred to plants

b. auxiliary brooders -- eggs remain attached to mom's belly

1) SA catfishes --vascularized stalk connects eggs to special "brood skin"

2) Syngathidae (pipefishes) -- male has brood skin

3) Pouch brooders - sea horses (Syngathidae); female extends oviduct into male pouch where eggs are fertilized and carried until able to swim (25-150 offspring)

4) Mouth brooders--sea catfishes, cichlids, bonytounges, cardinal fishes

--eggs generally large and yolky

--usually carried by females in cichlids, both sexes in some species

5) Gill chamber brooders-- NA cavefishes Amblyopsidae

6) Trophic provisioning - mucous secretions, trophic eggs

2. Internal Bearers--female only, internal fertilization, small number of eggs, large young

a. ovoviviparity -- eggs without supplemental nutrition

b. viviparity--eggs get supplemental nutrition during development

1) Chondrichthyes

--many species viviparous

--uterine milk (rays), placental viviparity (Carcharinidae)

--some lay embryos in capsule to complete development outside

--some have trophic eggs that are consumed by embryos

--embryonic cannibalization is known to occur in some species

2) Goodeidae, Poeciliidae

--true viviparity -- vascularized pericardial tissue loops around neck of embryo and maintains

close contact with ovarian wall

VII. Alternative Life-histories

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Updated 11 February 1999, J. Mygatt