Hermodice carunculata

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Transcript Hermodice carunculata

High degree of connectivity among amphi-Atlantic populations of Hermodice
carunculata (Amphinomidae, Annelida)
Joseph Ahrens, Elizabeth Borda, Alexandra Campbell, Anja Schulze
Texas A&M University at Galveston
Introduction:
Results/ Discussion:
Polychaete annelids in the genus Hermodice , commonly known as bearded fireworms (Fig. 1), are
facultative corallivores (Lewis, 2009) that inhabit reefs in the Atlantic Ocean, extending into the Gulf of
Mexico (GoM) as well as the Caribbean and the Mediterranean Seas. Their destructive feeding
behavior has been shown to stunt the branch growth of the hydrocoral Millepora complanata in the
Caribbean (Whitman, 1988). Additionally, in the Mediterranean, bearded fireworms serve as a winter
reservoir and vector for Vibrio shiloi, the pathogen responsible for the summer bleaching of Oculina
patagonica (Rosenberg and Falkovitz, 2004; Sussman et al., 2003).
Phylogenetic analyses supported the monophyly of amphi-Atlantic Hermodice (pp=0.99; boot=100) and
resulted in a tree consisting of two clades (Fig. 3), one indicating a private lineage of only Mediterranean
specimens (pp=1.0; boot=67%) and the other primarily containing samples from the Greater Caribbean
(pp=1.0; boot=58%). A subclade of the Greater Caribbean population was also strongly supported
(pp=1.0). These clades, however, showed weak bootstrap support and one of the Crete specimens
clustered with samples from the Greater Caribbean for both combined and independent COI and 16S
analyses.
A recent study determined that bearded fireworms found in the Greater Caribbean are
morphologically distinct from those in the Mediterranean and East Atlantic based on differences in
branchial filament abundance (Fig. 1, right), as well as anal lobe morphology (Yaῆez-Rivera and
Salazar-Vallejo, 2011). Hence, the genus Hermodice has been revised to include two species: H.
carunculata in the Greater Caribbean and west Atlantic, and H. nigrolineata in the Mediterranean.
However, no molecular data was used to support the delineation of amphi-Atlantic Hermodice species.
Preliminary mitochondrial COI analysis (this study) indicated low levels of divergence between
populations and revealed certain Mediterranean specimens that tend to cluster with a GoM
phylogroup. Therefore, a broader genetic study including samples from additional locales as well as
mitochondrial 16s rDNA sequence data has been conducted to determine whether the
aforementioned delineation of amphi-Atlantic Hermodice populations can be supported by molecular
evidence.
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Mean COI nucleotide distances ranged between 5.42 and 15.59 among GoM and Mediterranean
populations. Genetic distances ranged from 0.7 to 1.1% within populations and from 0.8 to 3.0% between
populations (Table 1). Analysis of Molecular Variance (AMOVA) for COI indicates that roughly 55% of
variation occurred among the GoM and Mediterranean groups, whereas 44% of variation occurred within
populations (Table 2).
Based on phylogenetic analyses as well as genetic distance calculations, the two amphi-Atlantic bearded
fireworm populations do not constitute separate species (according to the Phylogenetic Species
Concept). Therefore, the morphological distinction between Greater Caribbean and Mediterranean/ East
Atlantic Hermodice populations is not corroborated by molecular evidence. Whereas other genetic studies
of amphinomid polychaetes have revealed the presence of cryptic species complexes (Barroso et al.,
2004), our study indicates high population connectivity across a wide geographic range for H. carunculata.
0.5
1
0.99/100
Yucatan / Belize
Panama
Curaçao
British Virgin Islands
Bahamas / Florida Keys
Panama City, FL (GoM)
Sonnier Bank (GoM)
Flower Gardens Banks (GoM)
Malta
Crete
0.99/92
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Figure 1: Hermodice carunculata specimens collected from Sonnier Bank. Dorsal branchial filaments from H.
carunculata (right, top) and H. nigrolineata (right, bottom) from Yaῆez-Rivera and Salazar-Vallejo (2011).
Figure 3: 50% majority rule consensus tree constructed using Bayesian inference. Scale bar indicates percent divergence among
taxa. Posterior probability (BI)/ bootstrap values (MP) are shown for some clades. The subclade in the primarily Greater Caribbean
clade received high posterior probability but was unsupported by bootstrap analysis. Note the Mediterranean (Crete) outlier within the
Greater Caribbean clade.
Materials and Methods:
Collection: SCUBA divers hand collected live specimens from East Flower Garden Banks (EFGB),
West Flower Garden Banks (WFGB), Sonnier Bank, and Panama City, FL to represent the GoM
population. Caribbean specimens and sequence data were provided from Curaçao, the British
Virgin Islands and Bahamas. Mediterranean samples were taken from Crete and Malta. All
specimens were preserved in ethanol. Additional sequences for specimens from the Yucatan
Peninsula (n=4), Brazil (GenBank), Panama and the Florida Keys (n=2) were also included in the
phylogenetic analyses. (Fig. 2)
Figure 2: World map displaying sample sites for this study. Points are color-coded according to the legend shown in Figure 3.
Basemap taken from ArcGISOnline.
Topics for Future Research:
Acknowledgements:
Processing: Using standard protocols, a fragment of the cytochrome c oxidase subunit I (COI)
gene (~650bp) and 16srDNA (~450bp) was sequenced for 62 specimens. Sequences were
aligned using Mesquite (Maddison and Maddison, 2011) and exported for analysis.
An examination of the morphology of Mediterranean outliers will help to determine whether
there is a genetic basis for the morphological criteria used by Yaῆez-Rivera and Salazar-Vallejo
(2011).
Analysis: Two phylogenetic analyses were performed: Bayesian inference in MrBayes 3.1.2
(Huelsenbeck and Ronquist, 2002) as well as maximum parsimony using 500 bootstrap
pseudoreplicates in PAUP*v. 4.0a122 (Swofford, 2002). Bayesian analysis was run on servers
powered by CIPRES (Miller et al., 2010). Several amphinomid taxa were used as outgroups to
determine support values for the midpoint root, but were not included in the consensus tree.
Population genetic analyses for three GoM populations (EFGB, WFGB and Sonnier), Crete, and
Malta were conducted using Arlequin 3.5.1.2 (Excoffier et al., 2006). Genetic distances
(uncorrected) between populations were calculated in MEGA 4.1 (Tamura et al., 2007).
Histological analysis of bearded fireworms undergoing posterior regeneration will provide
insight into the developmental processes giving rise to the pygidium as well as important
accessory internal and external morphological features like the anal lobe and botryoidal
tissue.
We would like to thank the Research and Graduate Studies Office of TAMUG for funding this
project as well as the captain and crew of the M/V Fling for diving support. Thanks to Patrick
Schembri (Malta) and Sarah Faulwetter (Crete) for providing Mediterranean samples, Marissa
Nuttall and Brett Gonzalez for GoM specimens, Pat Krug (Bahamas), Gonzalo Giribet (Belize,
Florida Keys), Beatriz Yaῆez-Rivera (Yucatan, Mexico) and Alex Wolf (Curaçao). Ben Nguyen,
Andrew Nguyenba and Laura Timm provided additional support with sequencing.
Malta
Crete
EFGB
WFGB
Sonnier
Panama City
Curaçao
Virgin Islands Bahamas
Malta
0.008
6.24
15.59
13.25
15.22
Crete
0.009
0.010
12.80
11.01
12.48
EFGB
0.030
0.025
0.012
5.61
5.75
WFGB
0.025
0.021
0.012
0.009
5.42
Sonnier
0.028
0.023
0.010
0.010
0.009
Panama City
0.029
0.024
0.011
0.010
0.009
0.011
Curaçao
0.029
0.024
0.012
0.010
0.010
0.010
0.011
Virgin Islands
0.030
0.024
0.010
0.008
0.009
0.009
0.009
0.007
Bahamas
0.024
0.020
0.010
0.010
0.009
0.010
0.010
0.010
0.011
Table 1: Mean genetic (COI) distances between (bottom left) and within (diagonal) populations calculated in MEGA. The
mean number of (COI) nucleotide differences for the populations used in Arlequin analysis (top right) are also included.
Designing a short amplicon primer set and an unlabelled probe around an informative region
of COI or 16s rDNA for use in high resolution melting analysis (HRMA) will allow for fast and
inexpensive genotyping of Hermodice specimens from each of the two main clades.
Variation
d.f.
Sum of Squares
Variance Components
Percentage of
variation
Among groups
1
95.870
3.51027
Va
55.12
Among
Populations
Within Groups
3
10.213
0.06308
Vb
0.97
Within
Populations
58
165.437
2.85235
Vc
43.91
Total
62
271.519
6.49571
Table 2: AMOVA results for COI showing variation among Mediterranean (Crete, Malta) and GoM (EFGB,
WFGB, Sonnier) groups, among the populations within these groups, and within each population.
References:
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‘cosmopolitan’ wreworm, consists of at least three cryptic species. Marine Biology, 157, 69-80.
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authors.
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reservoir and spring-summer vector for the coral-bleaching pathogen vibrio shiloi. Environmental Microbiology, 5(4), 250255.
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