Life history patterns: many solutions to the same problem

Transcription

1 Life history patterns: many solutions to the same problem The problem: how to maximize reproductive success, given the uncertainties of mortality for adults and offspring At what age and size should I start to reproduce (males = females?) Large or small offspring? Many or few? Parental care or not? (parent-offspring conflict) When in the year to reproduce? Every year or not? How long to I plan on living?

2 Periodic: Large body, late maturation, high fecundity, low juvenile survival, high adult survival Mims et al Ecology of Freshwater Fishes. 19: Based on Winemiller Fecundity Opportunistic: small body, early maturation, low juvenile survival Equilibrium: -medium size, low fecundity, high juvenile survival

3 Life history patterns: How do salmonids compare with other fishes? 1. Length at maturity 2. Life span 3. Egg size and fecundity (number of eggs) 4. Spawning season 5. Hatching or emergence date Wootton (1984) assembled data on the life history patterns of 162 freshwater fish species in Canada, and this is the basis for comparison (with some updates on salmonids)

4 Length (mm) non-salmonids salmonids Age at maturity Conclusion: salmonids are average or below average in age, and above average in length.

5 Fecundity non-salmonids 100 salmonids Adult length (mm) Conclusion: salmonids have very few eggs, for their length, compared to other fishes.

6 Number of species non-salmonids salmonids > 6.0 Egg diameter (mm) Conclusion: salmonids have exceptionally large eggs

7 Early comment on spawning seasons Izaak Walton, The Compleat Angler, 1653 P. 68: the [brown] Trout usually spawns about October or November, but in some rivers a little sooner or later: which is the more observable, because most other fish spawn in the spring or summer, when the sun hath warmed both the earth and water, and made it fit for generation.

8 Number of species salmonids non-salmonids Month of spawning Conclusion: salmonids are among the very few fall spawning species (almost all the others are their relatives, the whitefishes, family Coregonidae).

9 Number of species non-salmonids salmonids > 200 Days to hatch Conclusion: salmonids have a very prolonged incubation period, and emerge in spring at about the same time as the progeny of spring-spawning fishes.

10 How do we explain such life history patterns as anadromy, semelparity, and age at maturity? Fitness can be defined as the sum, over the entire lifespan, of the probability of surviving to a given age (lx) times the reproductive potential at that age (bx). W = Σ (lx * bx) Consider the relative fitness of anadromous sockeye salmon and non-anadromous kokanee as a case in point.

11 Comparative hypothetical fitness of sockeye (3000 eggs) and kokanee (500 eggs) Age form length survival number fecundity fitness 1st spring kokanee sockeye st fall kokanee sockeye nd spring kokanee sockeye nd fall kokanee sockeye rd fall kokanee sockeye th fall kokanee sockeye

12 Comparative hypothetical fitness of sockeye (3000 eggs) and kokanee (500 eggs) Age form length survival number fecundity fitness 1st spring kokanee sockeye st fall kokanee sockeye nd spring kokanee sockeye nd fall kokanee sockeye rd fall kokanee sockeye th fall kokanee sockeye

13 Comparative hypothetical fitness of sockeye (3000 eggs) and kokanee (500 eggs) Age form length survival number fecundity fitness 1st spring kokanee sockeye st fall kokanee sockeye nd spring kokanee sockeye nd fall kokanee sockeye rd fall kokanee sockeye th fall kokanee sockeye

14 Comparative hypothetical fitness of sockeye (3000 eggs) and kokanee (500 eggs) Age form length survival number fecundity fitness 1st spring kokanee sockeye st fall kokanee sockeye nd spring kokanee sockeye nd fall kokanee sockeye rd fall kokanee sockeye th fall kokanee sockeye

15 Comparative hypothetical fitness of sockeye (3000 eggs) and kokanee (500 eggs) Age form length survival number fecundity fitness 1st spring kokanee sockeye st fall kokanee sockeye nd spring kokanee sockeye nd fall kokanee sockeye rd fall kokanee sockeye th fall kokanee sockeye

16 Comparative hypothetical fitness of sockeye (3000 eggs) and kokanee (500 eggs) Age form length survival number fecundity fitness 1st spring kokanee sockeye st fall kokanee sockeye nd spring kokanee sockeye nd fall kokanee sockeye rd fall kokanee sockeye th fall kokanee sockeye

17 Life history patterns The differences between salmonids and other fishes stem primarily from: 1. anadromy (resulting in fast growth), 2. semelparity (resulting in early age at maturity and high reproductive output), and 3. parental care (increasing survival of progeny in an otherwise harsh world). These are relatively unusual patterns, thus salmonids are not typical fishes.

18 Parental Care What are the benefits and costs? (If it is such a great idea, why doesn t everyone do it?) How prevalent is parental care in fishes? Is the salmonid pattern typical?

19 Parental Care Benefits: Increased survival of offspring Costs: Reduced breeding opportunities Reduced probability of surviving to breed again (predation, energy depletion)

20 Parental Care Parental care is practiced in 21% of the families of teleost (bony) fishes, and is more common in freshwater than marine fishes. In species with parental care, both parents provide care in 22% of the cases and one parent in 78%. Among the species with uni-parental care, males provide care in 61% of the cases vs. 39% for females. Why do salmon provide parental care, and why is the care provided by the female?

21 Diadromy Diadromy is the scheduled migration between freshwater and marine environments, and is distinguished from simple tolerance of intermediate salinities (i.e., euryhalinity). Anadromous fishes spawn in freshwater, offspring migrate to sea to rear, and return as adults to breed in freshwater. Catadromous fishes spawn at sea, offspring migrate to freshwater to rear, and return as adults to breed at sea. Amphidromous fishes spawn in freshwater, offspring migrate to sea to rear, then migrate back to freshwater for further rearing before breeding in freshwater.

22 Diadromous fishes Of all fishes, about 160 (0.8%) are diadromous. Anadromous fishes: about 87 species (54%), including salmonids, shad, striped bass, lamprey, smelt, sticklebacks, sturgeon, retropinnids, etc. Catadromous fishes: about 41 species (25%), including anguillid eels, galaxiids, etc. Amphidromous fishes: about 34 species (21%), including ayu, galaxiids, etc.

23 Striped bass, Morone saxatilis, is an anadromous species native to the east coast of North America. Adults spawn in rivers, larvae drift into and rear in estuaries, then migrate to coastal waters to grow until they breed.

24 American shad (Alosa sapidissima ) The Connecticut state fish

25 Atlantic eels (Anguilla anguilla and A. rostrata) are assumed to breed in deep waters of the Sargasso Sea. Eggs drift upward, and larvae travel in the Gulf Stream. Young glass eels ascend rivers and rear there for years before they mature, migrate to sea, breed and die. The classic example of a catadromous species

26 Galaxias fasciatus, the banded kokopu, is an amphidromous species from New Zealand. They spawn in streams in fall-winter, and the larvae are swept downstream. The juveniles rear at sea for about 4-5 months, then return to freshwater in spring. They feed and grow in streams for 2-3 years before breeding.

27 Geographic variation in diadromy Anadromy Percentage frequency Catadromy Amphidromy Latitude

28 Aquatic productivity and the presence of anadromy in fishes Anadromous fish species (%) Ocean productivity greater than FW productivity FW productivity greater than Ocean productivity Gross et al Science Log (ocean : freshwater) productivity