Biodiversity of FishesSex under Water

Rainer Froese

GEOMAR

06.02.14

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, active outside of male body

• Survival of gametes in water is short (few minutes), travel of sperms is short (few cm)

• Courtship and mating procedures aim to increase fertilization rate

Copyright restrictions may apply.

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

Vertebrate Sex through the AgesHagfish: keeping a secret for 600 million years

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

– Males have no penetrating organ – Cloacal gland may envelope sperms and eggs in slimy mass – Eggs found in females were not (yet?) fertilized

Lampreys (450 Million Years)

Genital papilla in males;

semelparous

Lungfishes (400 Million Years)

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

Coelacanths (400 Million years)

• Another secret: internal fertilization without special male organ (despite lobes)

• Young hatch from large eggs within the female; older embryos feed on unfertilized eggs; gestation takes 3 years (Froese & Palomares 2000)

Chimaeras (400 Million years)

• Finally: the advent of male intromittent organs (claspers) and separate urogenital openings

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

Sharks 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

Ray-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:

– Millions of small eggs– In-mouth fertilization and brooding (cichlids, Apogon)– Put eggs in other animal (bivalve, Rhodeus armarus,

ovipositor) – Outside of the water (Leuresthes tenuis)– Monogamy, polyandry, harems– Sex change (protogyny, protandry, simultaneous)– Cloning by self-fertilization (Kryptolebias marmoratus)– Cloning by gynogenesis (Poecilia formosa)

Synchronizing Release of Eggs and Sperm

• Parallel swimming, courtship, dancing, • Trial-spawning• Fake-eggs near male genital opening in female

mouthbrooders (e.g. Astatotilapia burtoni)• Genital tassel attracts mouthbrooding female to male’s

genital opening in Tilapia macrochir• Male bends around female and turns her on her back to

“squeeze” the eggs into bubble nest (Betta splendens)

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, size, and environment (check for online photos or video)