5. Reproduction and Recruitment Sexual vs Asexual Reproduction
Trends in reproductive ecology
What is recruitment?
Factors affecting recruitment
Process of larval habitat selection
FREE EGGS & SPERM
Fertilization FREE LARVAE
Common Slipper Limpet
Invasive species Europe Pacific Northwest Japan
Semelparous Single reproductive effort E.g., nudibranchs, polychaetes Iteroparous Multiple reproductive events E.g., Corals, seastars Asexual Reproduction
Produces offspring genetically identical to parent
Does not involve fertilization
Only one parent involved
Some swing both ways! Corals, fungi Asexual Reproduction Reproductive Effort It takes energy to reproduce Reproductive Effort
Metabolic energy spent reproducing… Searching for mates Copulation Gamete formation Fecundity = how many off spring you produce Fertilization mechanisms Brood protection & parental care General Development of Benthic Invertebrates
FREE EGGS & SPERM
Fertilization FREE LARVAE
ATTACHED ADULTS Development Types
Different types of larvae produced in benthic animals Planktotrophic Lecithotrophic Direct Development
Suitable for different strategies Dispersing long distances Surviving predators Settling fast Development Types
Planktotrophy Planktonic free living larvae No parental care Feeds in the plankton – phyto/zoo/bacteria/algae/DOM Special ciliary bands High fecundity In plankton – ~hrs to months Can travel V. long distances! High dispersal potential Delayed metamorphosis can be possible
Thorson, 1961; Jaekle & Manahan, 1989; Strathmann & Strathmann, 2007 Development Types Lecithotrophy Planktonic free living larvae
Do not feed in the plankton In plankton – ~hrs to days
Can also travel, but limited by food source Medium fecundity
Large yolky oocytes Evolutionary advantage
Brooding or egg masses
No free larvae
High parental care
Produces benthic juvenile
Esp in sessile organisms Development Types
Mixed Development Some brooding then a planktonic stage Parental protection & higher dispersal Best of both worlds??
Gallardo, 1977; Caswell, 1981 Development Time
More Reproductive Effort 500
Direct Higher chance K of survival
Egg Lecithotrophic Diameter (microns)
Planktotrophic r 0 0 50 Embryonic development time (days)
Todd and Doyle, 1981; Barnes & Hughes, 1998 r/K Selection Theory
r Selected K Selected Reproduce quickly Extensive parental care High fecundity Low fecundity Early maturation to adult Long maturation time Short life span Long life span Small body size Larger body size Unstable Environments Stable Environments Suitable for life in habitats Suitable for life in stable, that change over small unchanging environments time scales E.g. Corals, deep-sea E.g. Barnacles, organisms polychaetes Timing of Reproduction
When is a good time to reproduce? Energy Fixed amount of energy to an organism Growth & Reproduction Food to benthos can be seasonal Energy Allocation To Gametes Use food pulses to start reproduction To Larvae Use food pulses to feed larvae Timing of Reproduction
Eckelbarger & Watling (1995) 1 – Fast egg producers (immediate response to bloom) 2 – Slow egg producers (spawn when conditions favor larvae) 3 – Slow egg producers (use bloom to start repro) 4 – No relationship to bloom Trends in reproductive ecology Low Latitudes Planktonic development Planktotrophy
High Latitudes Direct development Lecithotrophy
Deep Sea Direct development
MANY EXCEPTIONS TO ALL OF THESE Thorson, 1950; Young, 1994; Grassle, 1994; Pearse, 1994; Rex & Waren, 1982 Settlement and Recruitment
Dispersive Larvae Broadcast Se lement spawning Recruitment Brooding
Direct Development Settlement/ Recruitment?
Attachment to benthos, metamorphosis into adults
Site critical for sessile organisms
Availability of larvae, settlement cues, hydrodynamic factors, larval behavior – all affect settlement
Number of organisms that settle and survive in a population
Operationally defined, e.g., it occurs when an organism is first detectable on a settling plate or in a colonization tray.
Cannot predict recruitment from reproduction Just because you have high fecundity doesn’t mean you have high recruitment Post-Settlement Mortality How can you predict recruitment?
Two long standing hypothesis Supply Side Ecology Populations limited by factors affecting adults Larval Habitat Selection Populations limited by habitat Lewin (1986), Young (1987) Supply Side Ecology
Space will not be occupied unless propagules get to it
Processes causing variation in arrival of recruits Production of larvae Fertilization Dispersal Transport, period of dispersal, mortality Oceanographic conditions Larval mortality Larval behavior Settlement Larval Habitat Selection
Much of early motivation for studying recruitment
Directed towards settlement
Main Issues Do larvae actively select habitat? If so, how?
Alternatives to Active Selection Passive Hydrodynamic dispersal and sorting Larvae and substrate have related characteristics (eg Stickiness) Larval Habitat Selection
3 Stages of Settlement
Stage 1 - Getting to/staying in vicinity of suitable habitat
Stage 2 - Getting to the bottom
Stage 3 - Staying on the bottom
Active processes could be useful in all these stages Conclusions
Many life histories amongst invertebrates Though there are trends, these are not rules
Though direct development is more evolutionary evolved, many advantages to pelagic development
Cannot infer recruitment from settlement Modified by post-settlement mortality
Larval arrival/retention often influenced by larval behavior
Interactions between benthic recruitment and water column processes in the field are poorly known References
Barnes, R.S.K. & Hughes, R.N. 1999. An introduction to marine ecology. Blackwell Science, Oxford.
Caswell, H. 1981. The evolution of “mixed” life histories in marine invertebrates and elsewhere. American Naturalist, 117: 529-536.
Gallardo, C.S. 1977. Two modes of development in the morphospecies Crepidula dilatata (Gastropoda: Calyptraeidae) from Southern Chile. Marine Biology, 39: 241-251.
Grassle, J.F. 1994. Ecological patterns in the deep-sea benthos: how are they related to reproduction, larval biology and recruitment. In: Young, C.M & Eckelbarger, K.J. (eds) Reproduction, larval biology and recruitment of the deep- sea benthos. Columbia University Press, New York. pp 306-314.
Jaeckle, W.B. & Manahan, D.T. 1989. Feeding by a “non-feeding” larva: uptake of dissolved amino acids from seawater by lecithotrophic larvae of the gastropod Haliotis rufescens. Marine Biology, 103: 87-94.
Levinton, J.S. 2001. Part II. Marine Organisms: Function and Environment. 5. Reproduction, dispersal and migration. In: Marine Biology. Oxford University Press, Oxford. References contd
Lewin, R. 1986. Supply – side ecology. Science, 234 (4772), 25-27.
Strathmann, M.F. & Strathmann, R.R. 2007. An extraordinarly long larval duration of 4.5 years from hatching to metamorphosis for teleplanic veligers of Fusitriton oregonensis.
Thorson, G. 1950. Reproductive and larval ecology of marine invertebrates. Biological Review, 25: 1-45.
Thorson, G. 1961. Length of pelagic larval life in marine bottom invertebrates as related to larval transport by ocean currents. In: Sears, M. (ed) Oceanography. American Association of Advanced Science (publ No 67), Washington D.C. pp 455-474
Pearse, J.S. 1994. Cold-water echinoderms break “Thorson’s rule”. In: Young, C.M. & Eckelbarger, J.K. (eds) Reproduction, larval biology and recruitment in the deep- sea benthos. Columbia University Press, New York. pp 26-43.
Rex, M.A. & Waren, A. 1982. Planktotrophic development in deep-sea prosobranch snails from western North Atlantic. Deep-Sea Research, 29: 171-184. References contd
Todd, C.D. & Doyle, R.W. 1981. Reproductive strategies of marine benthic invertebrates; a settlement-timing hypothesis. Marine Ecology Progress Series, 4: 75-83.
Young, C.M. Novelty of “supply-side ecology”. Science, 235: 415-416.
Young , C.M. 1994. A tale of two dogmas: the early history of deep-sea reproductive biology. In: Young, C.M & Eckelbarger, K. J. (eds) Reproduction, larval biology and recruitment of the deep-sea benthos. Columbia University Press, New York. pp 1-25.