WR Reproduction (9, 10) Flashcards
Ayling A.L. (1980) Patterns of sexuality, asexual reproduction and recruitment in some subtidal marine demospongiae. The Biological Bulletin 158, 271–282
Ayling A.L. (1980) Patterns of sexuality, asexual reproduction and recruitment in some subtidal marine demospongiae. The Biological Bulletin 158, 271–282
The study
- Investigated the patterns of sexuality and asexual reproduction in 10 species of subtidal Demospongiae [east coast of northern new zealand]
- Getting around difficulties of studying sponges by using subtidal rather than intertidal populations [subject to disturbance]
- Looked at reproductive activity over a 2-year period
- Measured potential reproductive output & compared to recruitment rates recorded from natural & artificial surfaces
- Aimed to quantify gamete populations & reproductive output related to larval release and settlement
- Collected tissue samples of thinly encrusting species
- Permanent buoys were set up as reference points for mapping the 6 locations of each species
- Each sponge was marked with a nail & a numbered tag attached
- Counted the numbers of reproductive elements from 2 individuals per species
Ayling A.L. (1980) Patterns of sexuality, asexual reproduction and recruitment in some subtidal marine demospongiae. The Biological Bulletin 158, 271–282
Should consider:
Should consider:
Whether they are viviparous with embryogenesis occuring within the adult OR oviparous with oocytes / zygotes released into the sea
Are sexual products released synchronously or asynchronously in individuals or the entire population?
What form of asexual reproduction is present? -> gemmule formation, budding, or fragmentation
Ayling A.L. (1980) Patterns of sexuality, asexual reproduction and recruitment in some subtidal marine demospongiae. The Biological Bulletin 158, 271–282
Information about sponges
> sponge species may have separate sexes, or partially separate sexes with varying numbers of hermaphroditic individuals
> other species = hermaphroditic, producing sperm & oocytes simultaneously, sequentially (protogyny or protandry), or alternating sexes
> sequential sex changes may occur in a single reproductive season or over consecutive years
Ayling A.L. (1980) Patterns of sexuality, asexual reproduction and recruitment in some subtidal marine demospongiae. The Biological Bulletin 158, 271–282
Findings
> some were found to be all hermaphrodites (ceractinomorph sponges) and others gonochoric & oviparous (tetractinomorph sponges)
In the tetractinomorph sponge populations = majority female & in 2 species no males were found
> were there was high levels of disturbance = more viviparous larvae [thought to be an adaptation to this habitat]
> the different reproductive strategies appeared to be related to the level of disturbance the sponges normally encountered
> Stylopus sp. = simultaneous hermaphrodite that incubates its larvae - larvae were covered with cilia except for the posterior pole (bare) = summer months
> Achinoe sp. = simultaneous hermaphrodite which incubates its larvae = reproductive period extended over most of the year (Feb to Nov) & across the two years, all the regularly sampled sponges reproduced
Sperm was present for the last 4 months only
> Ancorina alata = gonochoristic & oviparous, but in each year ~50% of the population was reproductively active
> the viviparous larvae of the thinly encrusting sponges took from 1-4 days to settle
> oviparous larvae of Polymastia sp = 15-20 days to settle
> recruitment rates were found to vary greatly between species
Ayling A.L. (1980) Patterns of sexuality, asexual reproduction and recruitment in some subtidal marine demospongiae. The Biological Bulletin 158, 271–282
critical evaluation
> a reason for a lack of studies on the reproductive patterns of sponges = difficult to monitor natural populations, e.g. most intertidal sponges are subject to considerable physical disturbance therefore affecting patterns of settlement, growth & reproduction
> difficult to monitor long-term due to fluctuating abundances of sponges
> small size = difficult to cut tissue samples
Reproduction in the deep sea brittle stars
LECTURE 12 - REPRODUCTION IN THE DEEP SEA
Schoener A. (1968) Evidence for reproductive periodicity in the deep sea. Ecology 49, 82–
The deep-sea environment has been considered to be relatively uniform (temperature, salinity, etc) therefore seasonal variation is unlikely to affect organisms HOWEVER young brittlestars collected along a transect have been shown to be more abundant in summer than winter or spring [mostly Ophiura ljungmani & Ophiomusium lymani]
Both species = dioecious
Brittle star - the study
Collected at various depths over a 2.5 yr period
Variation in gonad development is summarised for both species in a 7-month interval (summer months) - may then december
10 samples of each species
Should be kept in mind that small material may be lost before the sample is brought to the surface
Removed and measured gonads & presence of eggs notes
Brittle star - the findings
- O. ljungmani = average gonad length was greater in Dec than May, although the average specimen size was smaller -> evidence of energy trade-off???
- The presence of well-developed gonads in Dec not May suggests that reproduction doesn’t take place at a constant rate throughout the year, however the small number of samples with well-developed gonads suggests that it is not completely halted
- O. lymani = found differentiated gonads in both May and December samples, but it is not known if they were mature in either sample -> little to no difference in the sizes of gonads in the samples
- The similar size in May and Dec may indicate that there is no change in this period, or that the sample interval was not long enough to detect a change [critical analysis]
- The differences in gonadal changes may reflect metabolic differences between the two species
- → Although the data is not fully conclusive, it suggests a “periodic phenomenon in a fairly constant environment”
Fecundity and egg size - the paper
Fecundity & egg size
King M.G. and Butler A.J. (1985) Relationship of life-history patterns to depth in deep-water caridean shrimps (Crustacea: Natantia)
Fcundity and egg size - the study
Life-history variables were estimated and interspecific comparisons made between Parapandalus serratifrons, Plesionika longirostris, Heterocarpus ensifer, H. gibbosus, H. sibogae, H. laevigatus (Pandalidae) and Saron marmoratus (Hippolytidae) -> all w different depth distributions
It is proposed that adult predation decreases with increasing depth, allowing deeper-water species to have an extended lifespan, and increased degree of iteroparity (multiple reproductive cycles in a lifetime) & a corresponding increase in lifetime reproductive effort
Samples of deep-water shrimp were gathered using baited traps set up at a range of depths (Fiji) - 120 to 800m to encompass all target species
Growth data & estimates of the age at which females reach sexual maturity were used to estimate the reproductive lifespan of each species → subjective!!
Calculated as the difference between the total lifespan & age at sexual maturity
Ovigerous females were weighed before and after their eggs were removed to work out weight of eggs & counted … also used to estimate brood size
Reproductive effort = proportion of the resources available to individual that are allocated to reproduction (i.e. rather than growth)
Can be expressed as the weight of eggs as a percentage of total body weight
Fcundity and egg size - the findings
- Interspecifically, reproductive lifespan tended to increase with increasing depth of distribution
- Mean egg sizes of species increased with increasing depth
- Brood sizes increased inconsistently with depth
- Several variables determine effective reproductive success
- Iteroparity vs semelparity
- Age at first reproduction
- Life-span
- Length of breeding season
- Egg & brood size
- The length of reproductive lifespan increases with increasing depth
- The deeper-water Heterocarpus species = extended reproductive lifespan - more spawnings?
- Number of eggs carried was significantly related to carapace length in Heterocarpus sibogae BUT brood sizes didn’t significantly increase with increasing egg development therefore suggesting that egg loss during development is negligible
- Likely to be influenced by the area available for egg attachment & females capacity for obtaining, storing & converting resources for egg production
- Species of shrimp in deeper water appear to have greater longevity, to reach a larger maximum size, and to be iteroparous → allow them to have a “higher total lifetime reproductive effort”
- The larvae of deeper-water species are subjected to a greater range of water temperatures (as well as other environmental factors) during their vertical migration -> this may reduce the probability of larval survival [5C at 200m & 17C at 600m]
- Deeper water = large eggs … increased ability to withstand starvation & escape predation
- The probability of larval survival decreases with increasing depth
- & this is offset in part by the production of larger eggs & greater lifetime reproductive effort
- Predation reduces with increasing depths = adults in deeper water can therefore have a longer lifespan and iteroparity -> results in an increase in total lifetime reproductive investment with increasing depth distribution
- Iteroparity = multiple reproductive cycles over the course of its lifetime
- Semelparity = single reproductive episode before death
