Lecture 2

1. Lecture 2 Abiotic Influences on Distribution; Reproduction, Dispersal and Migration

2. Important Abiotic Influences on the Distribution of Marine Organisms • Temperature • Salinity • Dissolved oxygen • Light

3. Temperature • Temperature variation is common in marine environment • Latitudinal temperature gradient, regional differences • Marine species have thermal limits → geographic limits are fixed latitudinally • Seasonal temperature change • Maximal in mid-latitudes and lowest at high latitudes • Short term changes (e.g., weather changes, tidal changes) • Intertidal – usually much greater daily and seasonal temperature ranges

4. Vertical Temperature Gradients Open Tropical Ocean Shallow Temperate Ocean

5. Temperature Tolerance • Species evolve differences in temperature tolerance, e.g., Antarctic species may not be able to survive waters warmer than 10 °C • Intertidal species usually tolerate a broader range of temperatures • Populations living along a latitudinal gradient might evolve local physiological races, with different temperature responses • May be genetically different • May have just acclimated

6. Temperature Effects on Growth and Reproduction • Growth and reproduction occur over a narrower range of temperature within the survival range • Growth usually faster at higher temperatures • Organisms may grow more slowly but live longer in cooler waters • Low-latitude range is limited by maximum summer temp • High-latitude range is limited by minimum winter temp

7. Temperature and Reproduction • Many organisms only spawn or reproduce at certain temperatures • Temperature can determine whether some species will reproduce sexually or asexually • Temperature can determine sex of developing embryos

8. Temperature can Control Seasonal Variation in Abundance FIG. 4.11 Seasonal variation in the abundance of colonies of the bryozoan Bugulaneritinea in the northern Gulf of Mexico near the lowest latitudinal limit of its range. Because the organism is near the warm limit of its distribution, its abundance is greater in the colder part of the year. (Courtesy of M. Keough.)

9. Salinity • Definition: g of dissolved salts per 1000g of seawater; units are o/oo or ppt or psu (practical salinity unit) • Controlled by: *evaporation, sea-ice formation (↑ salinity) *precipitation, river runoff (↓ salinity) • Salinity in open ocean is 32 to 37 ppt

10. Latitudinal Salinity Gradient Excess of evaporation over precipitation in mid-latitudes Excess of precipitation over evaporation at equator

11. Salinity • Marine organisms generally tolerate a narrow range of salinity • Salinity can change rapidly, especially in nearshore environments • Marine organisms must maintain relatively constant chemical conditions within cell • Significant changes in cellular dissolved inorganics will affect function of proteins • Various coping mechanisms

12. Oxygen in Seawater • Oxygen from atmosphere dissolves in seawater at the sea surface • Decreases with increasing temperature and salinity • Also impacted by nutrient inputs • Dissolved oxygen content is a balance between mixing with atmosphere and other oxygen-rich water bodies (+) and photosynthesis (+) and respiration (-)

13. Oxygen in Seawater • Restriction of water circulation, decomposition of organic matter, and excess respiration can lead to anoxia (low oxygen levels) ksjtracker.mit.edu

14. Mississippi River Watershed

16. Oxygen • Some habitats are low on oxygen • Low tide for many intertidal animals • Within sediment: often anoxic pore water • Oxygen minimum layers in water column: where organic matter accumulates at some depths • Seasonaloxygen changes as in estuaries: hypoxic zones, “dead zones”

17. Responses to Low Oxygen Levels • Leave the area • Decrease activity levels → reduces oxygen requirements • Regulate oxygen consumption (oxygen concentration can reach a minimum where this is no longer possible) • Increase transport rates of water across gills • Increase retention efficiency • Changes in blood chemistry, oxygen-binding pigments Fig 4.16

18. Jubilee!

19. Jubilee! • Low-oxygen water on bay floor spreads into shallow waters due to a certain combination of wind direction, salinity, surface temperature, and tidal variation • Organisms present in the shallow waters get trapped between the shore and the advancing mass of low-oxygen water • Organisms are headed for the surface waters and waters very close to shore that usually have enough oxygen to support them for the short time frame of the jubilee

20. Jubilee! • Almost always occur with an incoming tide and an easterly wind • Usually occur in the hours just before dawn

21. Light • Light = energy distributed in many wavelengths • Light intensity declines with depth • Ultraviolet and infrared wavelengths strongly attenuate with depth • Surface light that is too intense can deactivate protein and DNA • Too little light can limit plant growth

22. Light • Supplies the energy used by autotrophs to convert inorganic matter into organic matter • Can play a major role in behavioral adaptations • Diurnal vertical migrations, migration to and from feeding grounds, predator detection, choosing mates

23. Reproduction, Dispersal, and Migration

24. Sex and Reproduction • SEX vs. REPRODUCTION • Species can reproduce without sex (asexually) • Clonal growth involving fission (ex. corals, encrusting sponges, bryozoans) • Budding of individuals (ex. jellyfish, Hydra) • Fragmentation (ex. Some corals, annelids)

25. How Does Asexual Reproduction Occur? • Budding- an offspring begins to form within or on a parent; the process is completed when the offspring breaks free and begins to grow on its own. The offspring is a miniature version of the parent. • Fission- an individual simply splits into two or more descendants. • Parthenogenesis- female offspring develop from unfertilized eggs. These offspring are genetically identical to the mother.

26. Asexual Reproduction • Descendants are genetically identical - clone • Colonial - individuals are genetically identical, comprise a module; each module may have arisen from a sexually formed zygote, which then underwent fission to asexually reproduce clone module

27. Asexual Reproduction • Pros: • Lacks the cost of sexual reproduction • Allows spread of a successful genotype (in that habitat) • Occurs at a faster rate than sexual reproduction • Cons: • No opportunity to spread to another habitat • Not much genetic diversity

28. Cost of Sexual Reproduction • Sex involves expenditure of energy and time to find mates, combat among males • So why even have sexual reproduction?

29. Sex and Genetic Diversity • Sex increases combinations of genes • Recombination produces variable gene combinations, meiosis enhances crossing over of chromosomes: new gene combinations and intragenic variants • Allows offspring to survive in a broader variety of habitats • Develop resistance to disease, parasites • Asexual reproduction = clones → must wait for mutations to occur

30. Sexual Selection vs. Natural Selection • Selection for extreme forms that breed more successfully - major claw of fiddler crabs, deer antlers, colors of male birds • Can involve selection for display coloration, enhanced combat structures • Female choice often involved; selection for fit males

31. Sexual Selection

32. Types of Sexuality • Separate sexes = gonochoristic • Requires a mechanism for sperm transfer • Can be direct or through shedding of sperm (and possibly eggs) into water • Hermaphroditism: individual can have male or female function, simultaneously or sequentially, during sexual maturity

33. Simultaneous Egg and sperm cells are active within a single individual at the same time Self-fertilization is rare Sequential Start sexual maturity as one sex and then change into the opposite sex Protandrous - first male, then female Protogynous - first female, then male Hermaphroditism

34. Simultaneous Hermaphroditism - Acorn barnacles Barnacle penis

35. Sequential Hermaphroditism • Protandry - size advantage model • Producing eggs costs more energy than producing sperm • Older/larger individuals have more available energy • Being male when young/small allows for potential for producing many offspring with little energy investment • Above a threshold size, females can parent more offspring because their available energy can produce more eggs Crassostreavirginica eastern oyster

36. Protogyny • Male function must result in more offspring when male is older and larger • Important when aggression is important in mating success, e.g., some fishes where males fight to maintain group of female mates Red grouper (Epinephelusmorio)

37. Dwarf Parasitic Males • Occurs in situations where it is difficult to find mates • May either attach to females or reside very close to them • Some males may be parasitic on the females

38. Factors in Reproductive Success • Percent investment in reproduction - reproductive effort • The more energy that is devoted to reproduction, the less there is available for growth • Age of first reproduction (generation time) • Predictability of reproductive success/Environmental uncertainty • Parental care • Juvenile versus adult mortality rate

39. Life History Theory • Tactics that maximize population growth • Evolutionary “tactics”: variation in reproductive effort, age of reproduction, whether to reproduce more than once • Presume that earlier investment in reproduction reduces resources available to invest in later growth and survival

40. Examples of Life History Tactics • Strong variability in success of reproduction: reproduce more than once • High adult mortality: earlier age of first reproduction, perhaps reproduce only once • Low adult mortality: later age of first reproduction, reproduce more than once

41. Example: Selection in a Fishery • Shrimp Pandalusjordani, protandrous • Danish, Swedish catch • 1930-1956 – stable, increased slowly • 1956- 1960 – catch tripled (2000  6300 ton/y)

42. Selection in a Fishery • Average body size of catch decreased • Threshold size of switching to females decreased • Females became rare due to fishing • New genetic variant appears that switches from male to female at a smaller size → produces more offspring • Natural selection for these variants → size of sex switch declines over time

43. Iteroparity vs. Semelparity • Iteroparity: Having multiple reproductive cycles over the course of a lifetime • Semelparity: Characterized by a single reproductive episode before death

44. Reproductive Tactics: r and K Selection • MacArthur and Wilson (1967) • r = Intrinsic (unlimited or exponential) rate of increase of a population • K = the carrying capacity of the environment Individuals

45. Reproductive Tactics: r and K Selection

46. Reproductive Tactics: r and K Selection

47. Reproductive Tactics: r and K Selection • Idea of r- and K-selection is a bit of an oversimplification • Not all species in an environment will be r- or K-selected • Environment may result in r-selection for some species (e.g., copepods), and result in K-selection for others (e.g., whales) • A species may have a combination of r- and K-selected traits (are an intermediate of the two types)

48. Survivorship Curves • Type I - high survival in early and middle life, followed a rapid decline in survivorship in later life (Ex. humans) (K-selected) • Type II -roughly constant mortality rate, regardless of age (Ex. Birds, squirrels) • Type III - the greatest mortality is experienced early on in life, with relatively low rates of death past early stages (Ex. oysters, octopi)

49. Sex - Factors in Fertilization • Planktonic sperm (and eggs in many cases): problem of timing, turbulence, polyspermy, specificity • Direct sperm transfer (spermatophores, copulation): problem of finding mates (e.g., barnacles, timing of reproductive cycle)

50. Timing of Sperm and Egg Release • Epidemic spawning - known in mussels, stimulus of one spawner causes other individuals to shed gametes • Mass spawning - known in coral species, many species spawn on single nights • Timing of spawning (also production of spores by seaweeds) at times of quiet water (slack high or low tide) to maximize fertilization rates. Also spawn in response to phytoplankton in water (ex. mussels)