INTRODUCTION
Twinning in odontocetes appears to be a rare occurrence but has been reported in several species upon examination of dead animals (González et al., Reference González, López and Benavente1999; Nakamatsu, Reference Nakamatsu2001; IJsseldijk et al., Reference IJsseldijk, Gröne, Hiemstra, Hoekendijk and Begeman2014). No reports exist of the survival of multiparous births in this sub-order, where uniparous births are the norm (Perrin & Donovan, Reference Perrin, Donovan, Perrin, Brownell and DeMaster1984).
MATERIALS AND METHODS
An adult female Atlantic white-sided dolphin (Lagenorhynchus acutus) was found stranded dead at Weyland Bay, near Kirkwall, Orkney, Scotland (58°59′18.5316″N −2°57′12.8448″W) on 3 October 2008. The animal was subjected to a standardized cetacean necropsy (Kuiken & García Hartmann, Reference Kuiken and García Hartmann1991) within 24 h of being reported. Routine bacterial cultures were performed on a selection of tissues and a range of tissues were examined histologically (Davison et al., Reference Davison, Barnett, Perrett, Dawson, Perkins, Deaville and Jepson2013). Age was estimated using methods adapted from Lockyer (Reference Lockyer, Donovan, Lockyer and Martin1993). The ovaries were fixed in formalin, weighed and sectioned at 1–2 mm intervals along the broad ligament. The presence of corpora lutea or albicantia scars (an indication of maturity) were recorded.
RESULTS
The carcase was in a good state of preservation with only slight decomposition. The animal weighed 130.5 kg, was 217 cm long, and had a girth measured cranial to the dorsal fin of 124 cm. Teeth ageing estimated the dolphin to be 12 years old. The mean of three standard blubber thickness measurements was 16 mm and the nutritive condition of the animal was moderate to poor (Kuiken & García Hartmann, Reference Kuiken and García Hartmann1991). Externally the animal was unremarkable with no obvious parasites or scars and no evidence of bruising within the blubber or sub cutis. The lungs showed asymmetry consistent with live stranding; hyperinflation of the left lung and hypostatic congestion of the right lung. Stable foam was present in the trachea and bronchi and ruptured small emphysematous bullae in the left lung. All sections of the stomach were empty.
Two corpora lutea (CL) were present on the left ovary associated with grossly normal twin male foetuses in the left uterine horn. The left ovary weighed 12.44 g, CL 1 measured 17.53 mm (Height), 16.71 mm (Length), 16.61 mm (Width) and CL 2 measured 17.73 mm (H), 12.81 mm (L), 14.60 mm (W). The right ovary weighed 2.69 g and no corpora lutea were present. No corpora albicantia were observed on either ovary.
Both foetuses had distinct grossly normal placentas and amniotic sacs and they were therefore probably dizygotic twins. Foetus A weighed 7.20 g, was 56 mm in length with a maximum girth of 43 mm. Foetus B was slightly larger weighing 8.00 g, 64 mm long with a maximum girth of 49 mm (Figure 1).
Twin Atlantic white-sided dolphin (Lagenorhynchus acutus) foetuses A and B.
An abscessed plerocercoid parasitic cyst (probably Monorygma grimaldii) was present in the mesovarium. There were no abnormalities noted within the vagina. There were multiple pale coloured fibrino-necrotic nodules present in the spleen. The remainder of the carcase was grossly unremarkable.
Brucella ceti was isolated from the liver, kidney, spleen, mesenteric lymph nodes and the mesovarium abscess in the dam suggesting a systemic distribution. Neither the foetuses nor placentas were subjected to bacteriological or histological examination.
Histological examination of tissues from the dam showed a variably mild to severe, sub-acute to chronic, generalized predominantly lymphocytic meningitis which increased in severity in a rostral to caudal direction. Haemorrhages were present throughout the brain, one relatively large forming a cavity in the cerebral cortex. Multiple necrotic foci and suppuration were present in the congested and haemorrhagic spleen, suggestive of early abscess formation, along with a mixed inflammatory cell sub-capsular and periportal hepatitis. Necrotic foci in the mesenteric lymph node contained eosinophils and occasional multi-nucleate giant cells (presumed parasitic). One lung was congested and oedematous (protein rich fluid within the lumina of both alveoli and bronchi). The other contained over-expanded alveoli with large numbers of erythrocytes within the lumina, consistent with live stranding (Kirkwood et al., Reference Kirkwood, Bennett, Jepson, Kuiken, Simpson and Baker1997). No significant lesions were found in the adrenals, kidneys, urinary bladder, heart, uterus or ovaries. These findings are consistent with a systemic B. ceti infection, the histological lesions present are consistent with those of neurobrucellosis in this and other species of pelagic delphinids (Davison et al., Reference Davison, Barnett, Perrett, Dawson, Perkins, Deaville and Jepson2013). This was considered to be the cause of the live stranding and the ultimate cause of death. The isolation of B. ceti from the mesovarium abscess would also suggest the infection involved the reproductive tract.
DISCUSSION
Atlantic white-sided dolphins become sexually mature at around 218 cm in length which corresponds to 6–8 years of age (Sergeant et al., Reference Sergeant, St. Aubin and Geraci1980; Rogan et al., Reference Rogan, Baker, Jepson, Berrow and Kiely1997). The gestation period in this species is believed to be 11 months with an oestrus cycle occurring during August and September with parturition in the following June and July (Robeck et al., Reference Robeck, Atkinson, Brook, Dierauf and Gulland2001). This would fit with the pregnancy status of 1–2 months in this animal. Ovulation and pregnancy occur asymmetrically and almost always in the left uterine horn in harbour porpoises (Phocoena phocoena) (Addink et al., Reference Addink, Sørensen and García Hartmann1995) and in bottlenose dolphins (Tursiops truncatus) where pregnancy occurs in the left horn 68% of the time (Harrison & Ridgeway, Reference Harrison and Ridgeway1971). The physiological mechanism for the observed asymmetry is unknown (Robeck et al., Reference Robeck, Atkinson, Brook, Dierauf and Gulland2001). It is not unreasonable to assume a similar frequency in Atlantic white-sided dolphins. Since the corpus luteum graviditatis is formed and preserved both in terms of size and activity throughout the pregnancy in most cetaceans (Slijper, Reference Slijper and Norris1966), and as the Atlantic white-sided dolphin in this study had two corpora lutea and two separate placentas, it is likely that this case of twinning resulted from a double ovulation (i.e. dizygotic twins).
Multiparous pregnancies have been described in several species of Mysticetes including sei whale (Balaenoptera borealis) (Gambell, Reference Gambell1968; Kawamura, Reference Kawamura1969); humpback whale (Megaptera novaeangliae) (conjoined twins; Zemsky & Budylenko, Reference Zemsky and Budylenko1970; and non-conjoined twins; Kimura, Reference Kimura1957); common minke whale (Balaenoptera acutorostrata) (conjoined twins; Zinchenko & Ivashin, Reference Zinchenko and Ivashin1987; and non-conjoined twins Kato, Reference Kato1982), Antarctic minke whale (Balaenoptera bonaerensis) (Kato, Reference Kato1982), blue whale (Balaenoptera musculus) (Branch, Reference Branch2008) and fin whale (Balaenoptera physalus) (Kimura, Reference Kimura1957; Laws, Reference Laws1961). Furthermore Jonsgård (Reference Jonsgård1953) reported a fin whale with six foetuses of varying sizes. Multiple foetuses are less frequent in Odontocetes than in Mysticetes (Lockyer, Reference Lockyer and Perrin1984), although they have been reported in sperm whales (Physeter macrocephalus) (Matsuura, Reference Matsuura1940; Ohsumi, Reference Ohsumi1965; Gambell, Reference Gambell1972; Best et al., Reference Best, Canham, Macleod, Perrin, Brownell and DeMaster1984; Clarke et al., Reference Clarke, Paliza and Van Waerebeek2011), short finned pilot whale (Globicephala macrorhynchus) (Escorza et al., Reference Escorza, Nakayama and Kawamura1994), striped dolphin (Stenella coeruleoalba) (Tobayama et al., Reference Tobayama, Uchida and Nishiwaki1970), bottlenose dolphin (Tursiops truncatus) (conjoined twins; Dabin et al., Reference Dabin, Cesarini, Clemenceau, Dhermain, Jauniaux, Van Canneyt and Ridoux2004; Kompanje, Reference Kompanje2005; Aytemiz et al., Reference Aytemiz, Danyer, Özgür Özbek, Tonay and Amaha Öztürk2014, and non-conjoined twins; Gray & Conklin, Reference Gray and Conklin1974; Lacave, Reference Lacave1991), Risso's dolphin (Grampus griseus) (Gassner & Rogan, Reference Gassner and Rogan1997), beluga whale (Delphinapterus leucas) (Osborn et al., Reference Osborn, Dalton, Dold and Robeck2012), short-beaked common dolphin (Delphinus delphis) (González et al., Reference González, López and Benavente1999), Dall's porpoise (Phocoenoides dalli) (Nakamatsu, Reference Nakamatsu2001) and harbour porpoise (IJsseldijk et al., Reference IJsseldijk, Gröne, Hiemstra, Hoekendijk and Begeman2014). Of these cases, the striped dolphin, sperm whale, common dolphin, Risso's dolphin, Dall's porpoise, harbour porpoise and conjoined twins of the bottlenose dolphins were free-living individuals that stranded dead, the others were all captive animals. The multiple pregnancy in the beluga followed artificial insemination (Osborn et al., Reference Osborn, Dalton, Dold and Robeck2012). To date, twinning had not been reported in any Lagenorhynchus sp.
All multiplets in the above studies were found in utero, and there are no records of the delivery of mature foetuses nor survival of twins in Mysticetes or Odontocetes (Perrin & Donovan, Reference Perrin, Donovan, Perrin, Brownell and DeMaster1984). In delphinid species an offspring's weight is approximately 10–15% that of the dam (Slijper, Reference Slijper and Norris1966). This high birth weight would not favour the survival of multiple foetuses and is likely to result in spontaneous abortion or death of the female (Perrin & Donovan, Reference Perrin, Donovan, Perrin, Brownell and DeMaster1984; IJsseldijk et al., Reference IJsseldijk, Gröne, Hiemstra, Hoekendijk and Begeman2014). Infection with Brucella is a well known cause of abortion and reproductive failure in terrestrial animals (Radostits et al., Reference Radostits, Gay, Hinchcliff and Constable2007) and Brucella sp. has been shown to cause placentitis and subsequent abortion in a bottlenose dolphin (Miller et al., Reference Miller, Adams, Ficht, Cheville, Payeur, Harley and Ridgeway1999). Although bacteriological and histological examination of the grossly normal reproductive tract and foetuses was not carried out in this case, isolation of B. ceti from the mesovarium abscess suggests the infection involved the reproductive tract. It is unlikely that, had the dam in this study lived, the twin foetuses would have survived to full term.
This was an adult sexually mature female, with no evidence of recent feeding along with gross and histological lesions consistent with systemic brucellosis including severe neurobrucellosis. The twins were an incidental finding in an animal that died of a systemic brucellosis infection. In conclusion, we believe this is the first report of twin foetuses in an Atlantic white-sided dolphin and furthermore the first in any Lagenorhynchus sp.
ACKNOWLEDGEMENTS
We would like to thank Lorraine Perrett, from the Department of Bacteriology and TB, Animal and Plant Health Agency (APHA), for confirming the Brucella isolate as B. ceti.
FINANCIAL SUPPORT
The postmortem investigation was carried out under the aegis of the UK Cetacean Strandings Investigation Programme, which is jointly funded by the Department for Environment Food and Rural Affairs (Defra) and the Scottish Government.
