Biodiversity of FishesSex under Water

Rainer Froese

IFM-GEOMAR

18.12.08

The Mechanics of Sex under Water

• Eggs have to be fertilized (or activated) by the right sperms

• Eggs are few and large (< 10 cm) or numerous and small (< 1 mm), internal, attached or drifting

• Sperms are very small, very numerous, mobile, outside

• Survival of gametes in water is short (few minutes)

• Courtship and mating aims to increase fertilization rate

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Powell, M. L. et al. Integr. Comp. Biol. 2005 45:158-165; doi:10.1093/icb/45.1.158

Vertebrate Sex through the Ages• Hagfish: keeping a secret for 600 million years

– Eggs are large (~ 4 cm) with horny shell, produced in batches of 20-30

– Males have no penetrating organ– Eggs found in females were not fertilized

Vertebrate Sex through the Ages Lampreys (450 Million Years)

Genital papilla in males

Vertebrate Sex through the Ages Lungfishes (400 Million Years)

• External fertilization of large eggs• Males guard eggs in burrow (Protopterus, Lepidosiren) • Eggs are deposited among plants (Neoceratodus)

Vertebrate Sex through the Ages Coelacanths (400 Million years)

• Another secret: internal fertilization without special male organ

• Young hatch from large eggs within the female, older embryos feed on unfertilized eggs, gestation takes 3 years

Vertebrate Sex through the AgesChimaeras (400 Million years)

• Finally: the advent of the male intromittent organ and the separate urogenital opening

• Females lay few, large (~10 cm), horny eggs

Vertebrate Sex through the AgesSharks and Rays (200 Million Years)

• Internal fertilization with claspers, but separate urogenital opening lost

• Few large young• From egg-laying (oviparity) to hatching after birth, to

hatching within the mother (viviparity), to a placenta-like arrangement

•Video start

Vertebrate Sex through the AgesRay-finned Fishes (150 Million Years)

• Separation of anus and urogenital opening• Wide variation in strategies for fertilization and

development of eggs and larvae• New strategies include:

– In-mouth fertilization and brooding (cichlids, Apogon)– In other animal (bivalve, Rhodeus armarus,

ovipositor) – Outside of the water (Leuresthes tenuis)– Sex change (protogyny, protandry, simultaneous)– Self-fertilization (Rivulus marmoratus)– Millions of small eggs

Indigo Hamlets

Mandarin fish

Video: http://www.youtube.com/watch?v=Tar9so2Jvfw

Sockeye salmon

Betta imbellis

Exercises

• In FishBase, select a species of your choice and discuss its reproductive strategy with respect to phylogeny and environment (check for online photos or video)