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Etherington GJ, Nash W, Ciezarek A, Mehta TK, Barria A, Peñaloza C, Khan MGQ, Durrant A, Forrester N, Fraser F, Irish N, Kaithakottil GG, Lipscombe J, Trong T, Watkins C, Swarbreck D, Angiolini E, Cnaani A, Gharbi K, Houston RD, Benzie JAH, Haerty W. Chromosome-level genome sequence of the Genetically Improved Farmed Tilapia (GIFT, Oreochromis niloticus) highlights regions of introgression with O. mossambicus. BMC Genomics 2022; 23:832. [PMID: 36522771 PMCID: PMC9756657 DOI: 10.1186/s12864-022-09065-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 12/05/2022] [Indexed: 12/23/2022] Open
Abstract
BACKGROUND The Nile tilapia (Oreochromis niloticus) is the third most important freshwater fish for aquaculture. Its success is directly linked to continuous breeding efforts focusing on production traits such as growth rate and weight. Among those elite strains, the Genetically Improved Farmed Tilapia (GIFT) programme initiated by WorldFish is now distributed worldwide. To accelerate the development of the GIFT strain through genomic selection, a high-quality reference genome is necessary. RESULTS Using a combination of short (10X Genomics) and long read (PacBio HiFi, PacBio CLR) sequencing and a genetic map for the GIFT strain, we generated a chromosome level genome assembly for the GIFT. Using genomes of two closely related species (O. mossambicus, O. aureus), we characterised the extent of introgression between these species and O. niloticus that has occurred during the breeding process. Over 11 Mb of O. mossambicus genomic material could be identified within the GIFT genome, including genes associated with immunity but also with traits of interest such as growth rate. CONCLUSION Because of the breeding history of elite strains, current reference genomes might not be the most suitable to support further studies into the GIFT strain. We generated a chromosome level assembly of the GIFT strain, characterising its mixed origins, and the potential contributions of introgressed regions to selected traits.
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Affiliation(s)
- G. J. Etherington
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - W. Nash
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - A. Ciezarek
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - T. K. Mehta
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - A. Barria
- grid.4305.20000 0004 1936 7988The Roslin Institute, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG UK
| | - C. Peñaloza
- grid.4305.20000 0004 1936 7988The Roslin Institute, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG UK
| | - M. G. Q. Khan
- grid.4305.20000 0004 1936 7988The Roslin Institute, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG UK ,grid.411511.10000 0001 2179 3896Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh, 2202 Bangladesh
| | - A. Durrant
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - N. Forrester
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - F. Fraser
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - N. Irish
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - G. G. Kaithakottil
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - J. Lipscombe
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - T. Trong
- grid.425190.bWorldFish, 10670 Penang, Malaysia
| | - C. Watkins
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - D. Swarbreck
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - E. Angiolini
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - A. Cnaani
- grid.410498.00000 0001 0465 9329Department of Poultry and Aquaculture, Institute of Animal Science, Agricultural Research Organization - Volcani Institute, Rishon LeTsiyon, Israel
| | - K. Gharbi
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK
| | - R. D. Houston
- grid.4305.20000 0004 1936 7988The Roslin Institute, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG UK ,Benchmark Genetics, 1 Pioneer Building, Edinburgh Technopole, Penicuik, EH26 0GB UK
| | | | - W. Haerty
- grid.421605.40000 0004 0447 4123Earlham Institute, Norwich Research Park, Colney Ln, Norwich, NR4 7UZ UK ,grid.8273.e0000 0001 1092 7967School of Biological Sciences, University of East Anglia, Norwich, UK
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Agha S, Mekkawy W, Ibanez-Escriche N, Lind CE, Kumar J, Mandal A, Benzie JAH, Doeschl-Wilson A. Breeding for robustness: investigating the genotype-by-environment interaction and micro-environmental sensitivity of Genetically Improved Farmed Tilapia (Oreochromis niloticus). Anim Genet 2018; 49:421-427. [PMID: 30058152 PMCID: PMC6175454 DOI: 10.1111/age.12680] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/09/2018] [Indexed: 12/03/2022]
Abstract
Robustness has become a highly desirable breeding goal in the globalized agricultural market. Both genotype‐by‐environment interaction (G × E) and micro‐environmental sensitivity are important robustness components of aquaculture production, in which breeding stock is often disseminated to different environments. The objectives of this study were (i) to quantify the degree of G × E by assessing the growth performance of Genetically Improved Farmed Tilapia (GIFT) across three countries (Malaysia, India and China) and (ii) to quantify the genetic heterogeneity of environmental variance for body weight at harvest (BW) in GIFT as a measure of micro‐environmental sensitivity. Selection for BW was carried out for 13 generations in Malaysia. Subsets of 60 full‐sib families from Malaysia were sent to China and India after five and nine generations respectively. First, a multi‐trait animal model was used to analyse the BW in different countries as different traits. The results indicate a strong G × E. Second, a genetically structured environmental variance model, implemented using Bayesian inference, was used to analyse micro‐environmental sensitivity of BW in each country. The analysis revealed the presence of genetic heterogeneity of both BW and its environmental variance in all environments. The presence of genetic variation in residual variance of BW implies that the residual variance can be modified by selection. Incorporating both G × E and micro‐environmental sensitivity information may help in selecting robust genotypes with high performance across environments and resilience to environmental fluctuations.
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Affiliation(s)
- S Agha
- The Roslin Institute, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, Edinburgh, UK.,Animal Production Department, Faculty of Agriculture, Ain Shams University, Shubra Alkhaima, 11241, Cairo, Egypt
| | - W Mekkawy
- Animal Production Department, Faculty of Agriculture, Ain Shams University, Shubra Alkhaima, 11241, Cairo, Egypt.,WorldFish, Jalan Batu Maung, Batu Maung, Bayan Lepas, 11960, Penang, Malaysia
| | - N Ibanez-Escriche
- The Roslin Institute, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, Edinburgh, UK.,Institute for Animal Science and Technology, Universitat Politècnica de València, 46022, València, Spain
| | - C E Lind
- WorldFish, Jalan Batu Maung, Batu Maung, Bayan Lepas, 11960, Penang, Malaysia
| | - J Kumar
- Rajiv Gandhi Center for Aquaculture, Vijayawada, Tamil Nadu, India
| | - A Mandal
- Rajiv Gandhi Center for Aquaculture, Vijayawada, Tamil Nadu, India
| | - J A H Benzie
- WorldFish, Jalan Batu Maung, Batu Maung, Bayan Lepas, 11960, Penang, Malaysia.,School of Biological Earth and Environmental Sciences, University College Cork, North Mall Campus, Cork, Ireland
| | - A Doeschl-Wilson
- The Roslin Institute, The University of Edinburgh, Easter Bush Campus, Midlothian, EH25 9RG, Edinburgh, UK
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Williams ST, Benzie JAH. EVIDENCE OF A BIOGEOGRAPHIC BREAK BETWEEN POPULATIONS OF A HIGH DISPERSAL STARFISH: CONGRUENT REGIONS WITHIN THE INDO-WEST PACIFIC DEFINED BY COLOR MORPHS, mt
DNA, AND ALLOZYME DATA. Evolution 2017; 52:87-99. [DOI: 10.1111/j.1558-5646.1998.tb05141.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/1996] [Accepted: 06/23/1997] [Indexed: 11/29/2022]
Affiliation(s)
- S. T. Williams
- Australian Institute of Marine Science; PMB 3 Townsville M.C. Qld 4810 Australia
- Department of Zoology and Tropical Ecology; James Cook University; Townsville Qld 4811 Australia
| | - J. A. H. Benzie
- Australian Institute of Marine Science; PMB 3 Townsville M.C. Qld 4810 Australia
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Lind CE, Kilian A, Benzie JAH. Development of Diversity Arrays Technology markers as a tool for rapid genomic assessment in Nile tilapia, Oreochromis niloticus. Anim Genet 2017; 48:362-364. [PMID: 28094451 DOI: 10.1111/age.12536] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/30/2016] [Indexed: 02/06/2023]
Abstract
The development of genomic markers is described for Nile tilapia, Oreochromis niloticus, using the Diversity Arrays Technology (DArT) genotype-by-sequencing platform. A total of 13 215 single nucleotide polymorphism (SNP) markers and 12 490 silicoDArT (dominant) markers were identified from broodstock of two selective breeding programs [Genetically Improved Farmed Tilapia (GIFT) strain from Malaysia and the Abbassa strain from Egypt]. Over 10 000 SNPs were polymorphic in either strain, and 2985 and 3087 showed strain-specific polymorphisms for the GIFT and Abbassa strains respectively. We demonstrate the potential utility of these markers for rapid genomic screening and use in breeding programs.
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Affiliation(s)
- C E Lind
- WorldFish, Jalan Batu Maung, 11960, Bayan Lepas, Penang, Malaysia
| | - A Kilian
- Diversity Arrays Technology Pty Ltd (DArT P/L), University of Canberra, Building 3, Bruce, ACT, 2617, Australia
| | - J A H Benzie
- WorldFish, Jalan Batu Maung, 11960, Bayan Lepas, Penang, Malaysia.,School of Biological Earth and Environmental Sciences, University College Cork, Cork, Ireland
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O'Farrell B, Benzie JAH, McGinnity P, Carlsson J, Eyto ED, Dillane E, Graham C, Coughlan J, Cross T. MHC-mediated spatial distribution in brown trout (Salmo trutta) fry. Heredity (Edinb) 2012; 108:403-9. [PMID: 21934705 PMCID: PMC3313050 DOI: 10.1038/hdy.2011.87] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2010] [Revised: 07/19/2011] [Accepted: 08/18/2011] [Indexed: 11/08/2022] Open
Abstract
Major histocompatibility complex (MHC) class I-linked microsatellite data and parental assignment data for a group of wild brown trout (Salmo trutta L.) provide evidence of closer spatial aggregation among fry sharing greater numbers of MHC class I alleles under natural conditions. This result confirms predictions from laboratory experiments demonstrating a hierarchical preference for association of fry sharing MHC alleles. Full-siblings emerge from the same nest (redd), and a passive kin association pattern arising from limited dispersal from the nest (redd effect) would predict that all such pairs would have a similar distribution. However, this study demonstrates a strong, significant trend for reduced distance between pairs of full-sibling fry sharing more MHC class I alleles reflecting their closer aggregation (no alleles shared, 311.5 ± (s.e.)21.03 m; one allele shared, 222.2 ± 14.49 m; two alleles shared, 124.9 ± 23.88 m; P<0.0001). A significant trend for closer aggregation among fry sharing more MHC class I alleles was also observed in fry pairs, which were known to have different mothers and were otherwise unrelated (ML-r = 0) (no alleles: 457.6 ± 3.58 m; one allele (422.4 ± 3.86 m); two alleles (381.7 ± 10.72 m); P<0.0001). These pairs are expected to have emerged from different redds and a passive association would then be unlikely. These data suggest that sharing MHC class I alleles has a role in maintaining kin association among full-siblings after emergence. This study demonstrates a pattern consistent with MHC-mediated kin association in the wild for the first time.
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Affiliation(s)
- B O'Farrell
- Microbial Phylogeography, Department of Microbiology, Environmental Research Institute, University College Cork, Cork, Ireland
| | - J A H Benzie
- School of Biological, Earth and Environmental Sciences, Environmental Research Institute, University College Cork, Cork, Ireland
| | - P McGinnity
- Aquaculture and Fisheries Development Centre (AFDC), School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland
- Marine Institute, Newport, Co. Mayo, Ireland
| | - J Carlsson
- Aquaculture and Fisheries Development Centre (AFDC), School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland
| | - E de Eyto
- Marine Institute, Newport, Co. Mayo, Ireland
| | - E Dillane
- Aquaculture and Fisheries Development Centre (AFDC), School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland
| | - C Graham
- School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland
| | - J Coughlan
- Aquaculture and Fisheries Development Centre (AFDC), School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland
| | - T Cross
- Aquaculture and Fisheries Development Centre (AFDC), School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland
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Forbes AT, Demetriades NT, Benzie JAH, Ballment E. Allozyme frequencies indicate little geographic variation among stocks of giant tiger prawn Penaeus monodon in the south-west Indian Ocean. ACTA ACUST UNITED AC 2010. [DOI: 10.2989/025776199784125881] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Affiliation(s)
- S. T. Williams
- Australian Institute of Marine Science, PMB 3, Townsville M.C. Qld 4810, Australia,
- Department of Zoological and Tropical Ecology. James Cook University, Townsville Qld 4811, Australia
| | - J. A. H. Benzie
- Australian Institute of Marine Science, PMB 3, Townsville M.C. Qld 4810, Australia,
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Uthicke S, Benzie JAH. Gene flow and population history in high dispersal marine invertebrates: mitochondrial DNA analysis of Holothuria nobilis (Echinodermata: Holothuroidea) populations from the Indo-Pacific. Mol Ecol 2003; 12:2635-48. [PMID: 12969467 DOI: 10.1046/j.1365-294x.2003.01954.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The sea cucumber, Holothuria nobilis, has a long-lived planktotrophic larvae, and previous allozyme surveys have suggested that high dispersal is realized. In contrast, recent ecological studies indicate that dispersal is low. To reconcile these data, and to investigate the evolution of this Indo-Pacific species, we screened geographical variation in 559 bp of a mitochondrial gene (COI) in 360 samples from the Australasian region and La Réunion. Sequences from La Réunion differed by > 7% from others and may constitute another species. Haplotype diversity in other samples was high (0.942, SD = 0.007), but haplotypes were closely related (mean nucleotide diversity: 0.0075, SD = 0.0041). AMOVA, pairwise FST values and exact tests did not detect significant population structure. Nested clade analysis showed that one of two main clades was over-represented in west Australia, whereas the other was more common in the northern Great Barrier Reef. Isolation-by-distance was identified as the main determinant of population structure at several clade levels. Contiguous range expansion was inferred for evolutionary older clade levels and this may correspond to a late Pleistocene (88 000-193 000 years ago) population expansion inferred from haplotype mismatch distributions. Thus, the population genetic structures detected are likely to be formed prior to the last ice age, with some indications for high dispersal on shorter time scales.
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Affiliation(s)
- S Uthicke
- Australian Institute of Marine Science, PMB no. 3, Townsville, Queensland 4810, Australia.
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Smith C, Benzie JAH, Wilson KJ. Isolation and characterization of eight microsatellite loci from silver-lipped pearl oyster Pinctada maxima. ACTA ACUST UNITED AC 2003. [DOI: 10.1046/j.1471-8286.2003.00377.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Benzie JAH, Ballment E, Forbes AT, Demetriades NT, Sugama K, Moria S. Mitochondrial DNA variation in Indo-Pacific populations of the giant tiger prawn, Penaeus monodon. Mol Ecol 2002; 11:2553-69. [PMID: 12453239 DOI: 10.1046/j.1365-294x.2002.01638.x] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Surveys of mitochondrial DNA (mtDNA) variation in the giant tiger prawn, Penaeus monodon, using restriction fragment length polymorphisms have provided the first clear evidence that the Indo-West Pacific region is a site of accumulation of genetic diversity rather than a site of origin of genetic diversity. No haplotyes were found in common between a group of five southeast African populations and a group of five Australian (including Western Australia) and three southeast Asian populations. The dominant haplotype was different in the Australian and southeast Asian population groups. Genetic diversity (pi) was greatest in Indonesia (pi averaged 0.05), less in the Philippines and Australia (pi averaged 0.01), and markedly less in the southeast African and the West Australian populations (pi averaged 0.003). The high diversity of the southeast Asian populations resulted from the occurrence in those populations of a set of haplotypes found only in southeast Asia but derived from the southeast African haplotypes. These genetic variants therefore evolved in the Indian Ocean and later migrated into the Indo-West Pacific region. Low genetic variation in the geographically marginal populations in southeast Africa and Western Australia is considered to be the result of bottlenecks, but mismatch distributions suggest that large population sizes have been maintained in Indonesian populations for long periods.
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Affiliation(s)
- J A H Benzie
- Australian Institute of Marine Science, PMB 3, Townsville, MC Queensland 4810, Australia.
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Williams ST, Benzie JAH. Evidence of a Biogeographic Break Between Populations of a High Dispersal Starfish: Congruent Regions Within the Indo-West Pacific Defined by Color Morphs, mtDNA, and Allozyme Data. Evolution 1998. [DOI: 10.2307/2410923] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Benzie JAH, Black KP, Moran PJ, Dixon P. Small-Scale Dispersion of Eggs and Sperm of the Crown-of-Thorns Starfish (Acanthaster planci) in a Shallow Coral Reef Habitat. Biol Bull 1994; 186:153-167. [PMID: 29281365 DOI: 10.2307/1542049] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The dispersal of eggs and sperm of crown-of-thorns starfish, Acanthaster planci (L.), was measured in the field using an array of collectors up to 10 m downstream of a spawning starfish. Hydrodynamic measurements, gamete dispersal numerical models, and the gamete cloud dispersal measurements for the first time quantified the relationship between hydrodynamic conditions and the dispersion of eggs and sperm in the field. In general, gamete concentrations fell rapidly and logarithmically with distance from the spawning starfish; egg concentrations at 3 m were 1% of those near the starfish. Simplified dispersal models showed a good correspondence with these field data, and confirmed the observation that eggs rose higher in the water column and spread more laterally at low current speeds over the short spatial scales being considered. Fertilization rates, predicted from laboratory measurements of fertilization success and the gamete concentrations measured in the field, were estimated to be 90-100% within 1 m and 70-100% at 10 m. These results are explained by high success rates of fertilization (fertilizing capacity) at the measured dilutions, and were similar to fertilization rates previously measured by others for crown-of-thorns starfish in the field. Although the eggs were observed to spread upwards into the water column due to turbulence, laboratory measurements of sinking rates showed eggs to be very slightly negatively buoyant (median fall velocity of 0.072 mm·s-1), whereas sperm were neutrally buoyant. A significant fraction of eggs also entered the seabed near the starfish; the proportion decreased with increasing current strength. This process may provide a mechanism for enhanced fertilization of these gametes and/or a mechanism for self-recruitment to a given reef population.
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Benzie JAH, Dixon P. The Effects of Sperm Concentration, Sperm:Egg Ratio, and Gamete Age on Fertilization Success in Crown-of-Thorns Starfish (Acanthaster planci) in the Laboratory. Biol Bull 1994; 186:139-152. [PMID: 29281364 DOI: 10.2307/1542048] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Laboratory experiments varying gamete concentrations and gamete age demonstrated significant reductions in fertilization success of the starfish Acanthaster planci (L.) with decreasing sperm concentration and increasing age of both eggs and sperm. The effect of aging in sperm was faster than that of eggs, and the speed of sperm aging increased with increasing dilution of sperm. Fertilization success was high over a wide range of sperm: egg ratios but declined rapidly at ratios less than 50, particularly at low sperm concentrations. A. planci gametes aged more slowly, and the loss of fertilizing capacity of sperm with dilution (the respiratory dilution effect) was far less, than in sea urchins. These characteristics provide a mechanism for enhanced fertilization success at given sperm concentrations and at greater distances and times from the point of gamete release, and may explain the higher fertilization rates achieved over longer distances in the wild by A. planci relative to sea urchins. Gametes would remain competent for longer periods at more dilute concentrations and so better achieve long-distance fertilization. Gametes obtained at the end of the breeding season were qualitatively different from those obtained early in the breeding season and showed reduced fertilization success for a given combination of variables, and different fertilization dynamics.
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