Fig 1.
This map has been elaborated using GIS software ArcGIS 10.4.
Fig 2.
Billie raising the newborn to the surface, and comparison of the bodyshape of the pregnant/not pregnant female bottlenose dolphin.
(A) On 11 August the female bottlenose dolphin was observed holding and pushing a newborn to the surface. The newborn showed folded fins and marked foetal folds. (B) Billie pregnant (28 July 2016). (C) Billie not pregnant (27 May 2017).
Fig 3.
Mixed group of mother/hybrid pair with common dolphins.
(A) The mother/hybrid pair and an adult common dolphin spotted on 6 October 2016; (B) Hybrid displaying jumps alongside a common dolphin separated by more than 10 m from the presumed mother on 4 September 2016.
Table 1.
Data regarding species group composition collected over 25 weeks (period 11 August 2016 to 29 May 2017).
Sightings were classified according to 19 descriptors: (A1) Common dolphins only; (A2) Striped dolphins only; (A3) Bottlenose dolphins only; (B1) Common dolphins with mother/hybrid pair together; (B2) Striped dolphins with mother/hybrid pair together; (B3) Bottlenose dolphins with mother/hybrid pair together; (C1) Common dolphins with mother/hybrid pair not together; (C2) Striped dolphins with mother/hybrid pair not together; (C3) Bottlenose dolphins with mother/hybrid pair not together; (D1) Common dolphins with one of the mother/hybrid pair (mother or hybrid); (D2) Striped dolphins with one of the mother/hybrid pair (mother or hybrid); (D3) Bottlenose dolphins with one of the mother/hybrid pair (mother or hybrid); (E1) Mother/hybrid pair only; (E2) Mother only; (E3) Hybrid only; (F1) Common mixed with striped dolphins; (F2) Common mixed with bottlenose dolphins; (F3) Bottlenose mixed with striped dolphins; (F4) Common and striped dolphins mixed with mother/hybrid pair.
Table 2.
Comparison of morphological features between species.
Morphological features of common dolphins (D. delphis), bottlenose dolphin (T. truncatus) (Mediterranean population) and the presumed hybrid, recorded in the Bay of Algeciras, south of Spain.
Fig 4.
Morphological features as coloration and shape patterns of the presumed hybrid.
(A) muted ‘criss-cross’ pattern typical of common dolphins, photographed 5 November 2016. (B) Creamy yellow patch on its side documented 7 February 2017; (C) light grey posterior flank on 20 February 2017; (D) Striped pattern on 20 February 2017; (E) Comparison between potential hybrid (top right) and common dolphin calf (bottom left). A similar ‘V’ shape and light-coloured dorsal fin can be observed in these dolphins. Documented on 20 February 2017.
Fig 5.
Coloration features displayed by D. delphis, T. truncatus, S. coeruleoalba and the hybrid calves.
Notice the similarities of colour patterns between (A) D. delphis, (B) T. truncatus and the hybrid (D). These similarities are absent when comparing features of (C) S. coeruleoalba (bluish-grey dorsally, white to light grey blaze on the flanks, eye-to-anus stripe that runs ventrally [55]) and the hybrid.
Fig 6.
Box plot analysis exposing medians, quartiles and confidence interval bars (95%) of data reported in Table 1, referred to 19 types (descriptors A1, A2 …F4) of sighting.
The extreme values (asterisks) are those that were more than three times the interquartile range from Q3. Outliers (white circles) are those that were located between 1.5 and 3 times the interquartile range from Q3. The figure clearly shows the close relationship of Billie and the newborn hybrid with common dolphins (B1), their relationships being completely nil with striped dolphins (A2) and with bottlenose dolphins (B3). The number of sightings of Billie and the newborn hybrid together in the absence of other dolphins also deserves mention (E1).
Table 3.
Registry table of hybridization between individuals of bottlenose dolphins (T. truncatus) in captivity and in the wild.